<?xml version="1.0" encoding="us-ascii"?><InstanceReport xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"><Version>2.4.0.8</Version><ReportLongName>0015 - Disclosure - 10. DEBT</ReportLongName><DisplayLabelColumn>true</DisplayLabelColumn><ShowElementNames>false</ShowElementNames><RoundingOption /><HasEmbeddedReports>false</HasEmbeddedReports><Columns><Column FlagID="0"><Id>1</Id><IsAbstractGroupTitle>false</IsAbstractGroupTitle><LabelSeparator>

</LabelSeparator><CurrencyCode /><FootnoteIndexer /><hasSegments>false</hasSegments><hasScenarios>false</hasScenarios><MCU><KeyName /><CurrencySymbol /><contextRef><ContextID>From2013-01-01to2013-06-30</ContextID><EntitySchema>http://www.sec.gov/CIK</EntitySchema><EntityValue>0001083712</EntityValue><PeriodDisplayName /><PeriodType>duration</PeriodType><PeriodStartDate>2013-01-01T00:00:00</PeriodStartDate><PeriodEndDate>2013-06-30T00:00:00</PeriodEndDate><Segments /><Scenarios /></contextRef><UPS /><CurrencyCode /><OriginalCurrencyCode /></MCU><CurrencySymbol /><Labels><Label Key="CalendarSupplement" Id="0" Label="6 Months Ended" /><Label Key="Calendar" Id="1" Label="Jun. 30, 2013" /></Labels></Column></Columns><Rows><Row FlagID="0"><Id>1</Id><IsAbstractGroupTitle>true</IsAbstractGroupTitle><LabelSeparator>

</LabelSeparator><Level>1</Level><ElementName>MBIS_DebtAbstract</ElementName><ElementPrefix>MBIS_</ElementPrefix><IsBaseElement>false</IsBaseElement><BalanceType>na</BalanceType><PeriodType>duration</PeriodType><IsReportTitle>false</IsReportTitle><IsSegmentTitle>false</IsSegmentTitle><IsCalendarTitle>false</IsCalendarTitle><IsEquityPrevioslyReportedAsRow>false</IsEquityPrevioslyReportedAsRow><IsEquityAdjustmentRow>false</IsEquityAdjustmentRow><IsBeginningBalance>false</IsBeginningBalance><IsEndingBalance>false</IsEndingBalance><IsReverseSign>false</IsReverseSign><FootnoteIndexer /><Cells><Cell FlagID="0" ContextID="" UnitID=""><Id>1</Id><IsNumeric>false</IsNumeric><IsRatio>false</IsRatio><DisplayZeroAsNone>false</DisplayZeroAsNone><NumericAmount>0</NumericAmount><RoundedNumericAmount>0</RoundedNumericAmount><NonNumbericText /><FootnoteIndexer /><CurrencyCode /><CurrencySymbol /><IsIndependantCurrency>false</IsIndependantCurrency><ShowCurrencySymbol>false</ShowCurrencySymbol><DisplayDateInUSFormat>false</DisplayDateInUSFormat></Cell></Cells><ElementDataType>xbrli:stringItemType</ElementDataType><SimpleDataType>string</SimpleDataType><IsTotalLabel>false</IsTotalLabel><UnitID>0</UnitID><Label>Debt</Label></Row><Row FlagID="0"><Id>2</Id><IsAbstractGroupTitle>false</IsAbstractGroupTitle><LabelSeparator>

</LabelSeparator><Level>2</Level><ElementName>us-gaap_DebtDisclosureTextBlock</ElementName><ElementPrefix>us-gaap_</ElementPrefix><IsBaseElement>true</IsBaseElement><BalanceType>na</BalanceType><PeriodType>duration</PeriodType><IsReportTitle>false</IsReportTitle><IsSegmentTitle>false</IsSegmentTitle><IsCalendarTitle>false</IsCalendarTitle><IsEquityPrevioslyReportedAsRow>false</IsEquityPrevioslyReportedAsRow><IsEquityAdjustmentRow>false</IsEquityAdjustmentRow><IsBeginningBalance>false</IsBeginningBalance><IsEndingBalance>false</IsEndingBalance><IsReverseSign>false</IsReverseSign><FootnoteIndexer /><Cells><Cell FlagID="0" ContextID="From2013-01-01to2013-06-30" UnitID=""><Id>1</Id><IsNumeric>false</IsNumeric><IsRatio>false</IsRatio><DisplayZeroAsNone>false</DisplayZeroAsNone><NumericAmount>0</NumericAmount><RoundedNumericAmount>0</RoundedNumericAmount><NonNumbericText>&lt;p style="font: 8pt/normal Times New Roman, Times, Serif; margin: 0; text-align: justify; text-indent: 0.5in"&gt;On May 29, 2009,
Mediabistro entered into a loan agreement in the amount of $7.2 million with the Company&amp;#146;s Chief Executive Officer, Alan
M. Meckler (the &amp;#147;2009 Meckler Loan&amp;#148;).&lt;/p&gt;

&lt;p style="font: 8pt/normal Times New Roman, Times, Serif; margin: 0; text-align: justify; text-indent: 0.5in"&gt;&amp;#160;&lt;/p&gt;

&lt;p style="font: 8pt/normal Times New Roman, Times, Serif; margin: 0; text-align: justify; text-indent: 0.5in"&gt;In conjunction
with the 2009 Meckler Loan, the Company (1) entered into a promissory note jointly and severally payable by the Company and
its subsidiary, Mediabistro.com Subsidiary Inc. (&amp;#147;MB Subsidiary&amp;#148;), to Mr. Meckler (the &amp;#147;2009 Note&amp;#148;), (2)
entered into a Security Agreement by and between the Company and Mr. Meckler (the &amp;#147;Security Agreement&amp;#148;) pursuant to
which the Company granted to Mr. Meckler a security interest in the Company&amp;#146;s assets, (3) entered into an Intellectual
Property Security Agreement by and between the Company and Mr. Meckler (the &amp;#147;IP Security Agreement&amp;#148;) pursuant to
which the Company granted to Mr. Meckler a security interest in the Company&amp;#146;s intellectual property, (4) entered into a
Pledge Agreement by the Company in favor of Mr. Meckler (the &amp;#147;Pledge Agreement&amp;#148;) pursuant to which the Company
granted to Mr. Meckler a security interest in and an assignment of all of the shares of stock or other equity interest of MB
Subsidiary owned by the Company, and (5) agreed to enter into a Blocked Account Control Agreement by and among the Company,
Mr. Meckler and a depositary bank, to further secure the Note (the &amp;#147;Control Agreement&amp;#148; and together with the 2009
Note, the Security Agreement, the IP Security Agreement and the Pledge Agreement, the &amp;#147;Company Loan
Documents&amp;#148;).&lt;/p&gt;

&lt;p style="font: 8pt/normal Times New Roman, Times, Serif; margin: 0; text-align: justify; text-indent: 0.5in"&gt;&amp;#160;&lt;/p&gt;

&lt;p style="font: 8pt/normal Times New Roman, Times, Serif; margin: 0; text-align: justify; text-indent: 0.5in"&gt;Simultaneously,
MB Subsidiary (1) entered into a Security Agreement by and between MB Subsidiary and Mr. Meckler pursuant to which
MB Subsidiary granted to Mr. Meckler a security interest in MB Subsidiary&amp;#146;s assets (the &amp;#147;MB Subsidiary
Security Agreement&amp;#148;), (2) entered into an Intellectual Property Security Agreement by and between MB Subsidiary and Mr.
Meckler pursuant to which MB Subsidiary granted to Mr. Meckler a security interest in MB Subsidiary&amp;#146;s intellectual
property (the &amp;#147;MB Subsidiary IP Security Agreement&amp;#148;), and (3) agreed to enter into a Blocked Account Control
Agreement by and among MB Subsidiary, Mr. Meckler and a depositary bank, to further secure the 2009 Note (the &amp;#147;MB
Subsidiary Control Agreement&amp;#148; and, together with the MB Subsidiary Security Agreement and the MB Subsidiary IP Security
Agreement, the &amp;#147;MB Subsidiary Documents&amp;#148;).&lt;/p&gt;

&lt;p style="font: 8pt/normal Times New Roman, Times, Serif; margin: 0; text-align: justify; text-indent: 0.5in"&gt;&amp;#160;&lt;/p&gt;

&lt;p style="font: 8pt/normal Times New Roman, Times, Serif; margin: 0; text-align: justify; text-indent: 0.5in"&gt;To fund the 2009
Meckler Loan, Mr. Meckler used a portion of the proceeds of a residential mortgage loan that Bank of America, N.A. (&amp;#147;BOA&amp;#148;)
granted to Mr. Meckler and Mrs. Ellen L. Meckler (the &amp;#147;BOA Loan&amp;#148;). Pursuant to a Collateral Assignment of the 2009
Note dated May 29, 2009, by Mr. Meckler to BOA, Mr. Meckler collaterally assigned the Note to BOA as additional collateral for
the BOA Loan. Payment terms of the 2009 Meckler Loan reflect pass through of the BOA Loan payment terms (excluding those funds
borrowed pursuant to the BOA Loan for Mr. Meckler&amp;#146;s personal use). As a result, the interest rate, amortization schedule
and maturity date of each loan are identical.&lt;/p&gt;

&lt;p style="font: 8pt/normal Times New Roman, Times, Serif; margin: 0; text-align: justify; text-indent: 0.5in"&gt;&amp;#160;&lt;/p&gt;

&lt;p style="font: 8pt/normal Times New Roman, Times, Serif; margin: 0; text-align: justify; text-indent: 0.5in"&gt;On September 1, 2010,
Mediabistro entered into a Note Modification Agreement with Mr. Meckler.&amp;#160;&amp;#160;The Note Modification Agreement reduced the
interest rate of the 2009 Note from 4.7% to 3.4% per annum.&amp;#160;&amp;#160;Interest on the outstanding principal amount is due and
payable on the first day of each calendar month through June 2014. Thereafter, principal and interest is due and payable in equal
monthly payments in an amount sufficient to pay the loan in full based on an amortization term of 15 years.&amp;#160;&amp;#160;In addition
to the interest rate reduction noted above, the Note Modification Agreement also reduced the required minimum monthly principal
and interest payments that commence on July 1, 2014.&amp;#160;&amp;#160;&lt;/p&gt;

&lt;p style="font: 8pt/normal Times New Roman, Times, Serif; margin: 0; text-align: justify; text-indent: 0.5in"&gt;&amp;#160;&lt;/p&gt;

&lt;p style="font: 8pt/normal Times New Roman, Times, Serif; margin: 0; text-align: justify; text-indent: 0.5in"&gt;On November 14, 2011,
the Company and MB Subsidiary entered into a 2&lt;sup&gt;nd&lt;/sup&gt; Note Modification Agreement with Mr. Meckler.&amp;#160;&amp;#160;The 2&lt;sup&gt;nd&lt;/sup&gt;
Note Modification Agreement amends the 2009 Note, which is described above.&amp;#160;&amp;#160;Under the 2&lt;sup&gt;nd&lt;/sup&gt; Note Modification
Agreement, the parties agreed to terminate the Company&amp;#146;s obligation to make a monthly accommodation fee of $40,000 to Mr.
Meckler.&amp;#160;&amp;#160;As a result, the 2&lt;sup&gt;nd&lt;/sup&gt; Note Modification Agreement reduces the effective interest payable on the 2009
Meckler Loan by $480,000 per year.&amp;#160;&amp;#160;The Company granted Mr. Meckler a fully vested stock option to purchase 142,858 shares
of the Company&amp;#146;s common stock (after giving effect to the August 16, 2012 one-for-seven reverse stock split) pursuant to
the terms of the 2008 Mediabistro Stock Option Plan.&amp;#160;&amp;#160;All other terms of the 2009 Meckler Loan remain unchanged.&lt;/p&gt;

&lt;p style="font: 8pt/normal Times New Roman, Times, Serif; margin: 0; text-align: justify; text-indent: 0.5in"&gt;&amp;#160;&lt;/p&gt;

&lt;p style="font: 8pt/normal Times New Roman, Times, Serif; margin: 0; text-align: justify; text-indent: 0.5in"&gt;Also on
November 14, 2011, Mediabistro&amp;#160;&amp;#160;and its wholly owned subsidiaries, MB Subsidiary and Inside Network: (1) entered
into a promissory note jointly and severally payable by the Company, MB Subsidiary and Inside Network to Mr. Meckler (the
&amp;#147;2011 Note&amp;#148;); (2) entered into a Security Agreement by and between the Company and Mr. Meckler (the &amp;#147;MBIS
Security Agreement&amp;#148;) pursuant to which the Company granted to Mr. Meckler a security interest in the Company&amp;#146;s
assets; (3) entered into an Intellectual Property Security Agreement by and between the Company and Mr. Meckler (the
&amp;#147;2&lt;sup&gt;nd&lt;/sup&gt; IP Security Agreement&amp;#148;) pursuant to which the Company granted to Mr. Meckler a security interest in
the Company&amp;#146;s intellectual property; and (4) entered into a Pledge Agreement by the Company in favor of Mr. Meckler (the
&amp;#147;2&lt;sup&gt;nd&lt;/sup&gt; Pledge Agreement&amp;#148;), and together with the 2011 Note, the MBIS Security Agreement and the
2&lt;sup&gt;nd&lt;/sup&gt; IP Security Agreement, (the &amp;#147;2011 Company Loan Documents&amp;#148;) pursuant to which the Company granted to
Mr. Meckler a security interest in and assignment of all of the shares of stock or other equity interest of MB Subsidiary and
Inside Network owned by the Company.&lt;/p&gt;

&lt;p style="font: 8pt/normal Times New Roman, Times, Serif; margin: 0; text-align: justify; text-indent: 0.5in"&gt;&amp;#160;&lt;/p&gt;

&lt;p style="font: 8pt/normal Times New Roman, Times, Serif; margin: 0; text-align: justify; text-indent: 0.5in"&gt;In the 2011 Note,
Mr. Meckler loaned the Company $1,750,000 (the &amp;#147;2011 Meckler Loan&amp;#148;).&amp;#160;&amp;#160;The interest rate of the 2011 Note
at the time of the loan was 3.10% per annum.&amp;#160;&amp;#160;Interest on the outstanding principal amount is due and payable monthly
until August 2014.&amp;#160;&amp;#160;Thereafter, principal and interest is due and payable in equal monthly installments, with the outstanding
principal amount, together with all accrued interest thereon, due and payable on August 18, 2016.&amp;#160;&amp;#160;The 2011 Note may
be prepaid at any time without penalty or premium.&lt;/p&gt;

&lt;p style="font: 8pt/normal Times New Roman, Times, Serif; margin: 0; text-align: justify; text-indent: 0.5in"&gt;&amp;#160;&lt;/p&gt;

&lt;p style="font: 8pt/normal Times New Roman, Times, Serif; margin: 0; text-align: justify; text-indent: 0.5in"&gt;In partial consideration
of the 2011 Note and the 2&lt;sup&gt;nd&lt;/sup&gt; Note Modification Agreement, Inside Network entered into a Security Agreement by and between
Inside Network and Mr. Meckler pursuant to which Inside Network granted to Mr. Meckler a security interest in Inside Network&amp;#146;s
assets (the &amp;#147;Inside Network Security Agreement&amp;#148;) to secure Inside Network&amp;#146;s obligations under the 2011 Note and
the 2009 Note.&lt;/p&gt;

&lt;p style="font: 8pt/normal Times New Roman, Times, Serif; margin: 0; text-align: justify; text-indent: 0.5in"&gt;&amp;#160;&lt;/p&gt;

&lt;p style="font: 8pt/normal Times New Roman, Times, Serif; margin: 0; text-align: justify; text-indent: 0.5in"&gt;The 2011 Company
Loan Documents and the Inside Network Security Agreement contain customary terms for a loan transaction of this type.&amp;#160;&amp;#160;In
an Event of Default (as defined in the 2011 Note) occurs and is continuing beyond a specified cure period, Mr. Meckler may declare
the 2011 Meckler Loan immediately due and payable. The 2011 Meckler Loan also will become immediately due and payable upon certain
events of bankruptcy or insolvency or in the event of a Change of Control (as defined in the 2011 Note) of MB Subsidiary, Inside
Network, or the Company.&lt;/p&gt;

&lt;p style="font: 8pt/normal Times New Roman, Times, Serif; margin: 0; text-align: justify; text-indent: 0.5in"&gt;&amp;#160;&lt;/p&gt;

&lt;p style="font: 8pt/normal Times New Roman, Times, Serif; margin: 0; text-align: justify; text-indent: 0.5in"&gt;On July 27, 2012,
the Company entered into a 3&lt;sup&gt;rd&lt;/sup&gt; Note Modification Agreement with Mr. Meckler that reduces the interest rate (i) of the
2009 Note to 2.975% from 3.40% effective June 1, 2012, and (ii)&amp;#160;of the 2011 Note to 2.40% from 3.10% effective on June 18,
2012.&amp;#160; All other terms of the promissory notes remain unchanged.&amp;#160;&lt;/p&gt;

&lt;p style="font: 8pt/normal Times New Roman, Times, Serif; margin: 0; text-align: justify; text-indent: 0.5in"&gt;&amp;#160;&lt;/p&gt;

&lt;p style="font: 8pt/normal Times New Roman, Times, Serif; margin: 0; text-align: justify; text-indent: 0.5in"&gt;Interest expense
on the 2009 Meckler Loan and 2011 Meckler Loan was $54,000 and $108,000 during the three and six months ended June 30, 2013, respectively,
and $64,000 and $127,000 during the three and six months ended June 30, 2012, respectively. There are no future minimum principal
payments due under the 2009 Meckler Loan and the 2011 Meckler Loan for the year ended December 31, 2013.&amp;#160;&amp;#160;There are future
minimum payments due to Mr. Meckler for the 2009 Meckler Loan and the 2011 Meckler Loan in the amount of $189,000 for the year
ended December 31, 2014; $419,000 for the year ended December 31, 2015; and $7.0 million for the year ended December 31, 2016.&lt;/p&gt;

&lt;p style="font: 8pt/normal Times New Roman, Times, Serif; margin: 0; text-align: justify; text-indent: 0.5in"&gt;&amp;#160;&lt;/p&gt;</NonNumbericText><FootnoteIndexer /><CurrencyCode /><CurrencySymbol /><IsIndependantCurrency>false</IsIndependantCurrency><ShowCurrencySymbol>false</ShowCurrencySymbol><DisplayDateInUSFormat>false</DisplayDateInUSFormat></Cell></Cells><ElementDataType>nonnum:textBlockItemType</ElementDataType><SimpleDataType>na</SimpleDataType><ElementDefenition>The entire disclosure for information about short-term and long-term debt arrangements, which includes amounts of borrowings under each line of credit, note payable, commercial paper issue, bonds indenture, debenture issue, own-share lending arrangements and any other contractual agreement to repay funds, and about the underlying arrangements, rationale for a classification as long-term, including repayment terms, interest rates, collateral provided, restrictions on use of assets and activities, whether or not in compliance with debt covenants, and other matters important to users of the financial statements, such as the effects of refinancing and noncompliance with debt covenants.</ElementDefenition><ElementReferences>Reference 1: http://www.xbrl.org/2003/role/presentationRef

 -Publisher FASB

 -Name Accounting Standards Codification

 -Topic 505

 -SubTopic 10

 -Section 50

 -Paragraph 3

 -URI http://asc.fasb.org/extlink&amp;oid=6928386&amp;loc=d3e21475-112644



Reference 2: http://www.xbrl.org/2003/role/presentationRef

 -Publisher SEC

 -Name Regulation S-X (SX)

 -Number 210

 -Section 02

 -Paragraph 19, 20, 22

 -Article 5



Reference 3: http://www.xbrl.org/2003/role/presentationRef

 -Publisher FASB

 -Name Accounting Standards Codification

 -Topic 210

 -SubTopic 10

 -Section S99

 -Paragraph 1

 -Subparagraph (SX 210.5-02.19,20,22)

 -URI http://asc.fasb.org/extlink&amp;oid=6877327&amp;loc=d3e13212-122682



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