Common IRS Terminology & Acronyms

Customer support specialists encounter dozens of acronyms every shift. Use this glossary for fast clarification.

Core Account Concepts

Term	Full Name	Definition
TIN	Taxpayer Identification Number	Generic term for SSN, ITIN, or EIN.
SSN	Social Security Number	9-digit number for individuals (XXX-XX-XXXX).
ITIN	Individual Taxpayer Identification Number	Issued to individuals not eligible for SSN (9XX-XX-XXXX).
EIN	Employer Identification Number	9-digit number for business entities (XX-XXXXXXX).
IMF	Individual Master File	The IRS database recording all individual taxpayer accounts (Form 1040 series).
BMF	Business Master File	The IRS database recording business accounts (Forms 941, 1120, 1065, etc.).
MFT	Master File Tax Code	2-digit code identifying the tax type (e.g., MFT 30 = Form 1040).
Tax Period / TXPD	Tax Period Ending	Year and month the tax year ends (e.g., 202412 for Dec 2024).
Module	Tax Module	The specific unit of work for one taxpayer, one tax form (MFT), and one tax period.
IRM	Internal Revenue Manual	Official guidelines, policies, and procedural handbook for IRS employees.

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Master File Tax (MFT) Codes

MFT Code	Form Name	Description
30	Form 1040	Individual Income Tax
01	Form 1120	Corporate Income Tax
02	Form 1065	Partnership Return
10	Form 941	Employer's Quarterly Federal Tax Return
11	Form 940	Employer's Annual Federal Unemployment (FUTA)
16	Form 1041	Estates and Trusts Income Tax
55	Various	Civil Penalties

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Operational Acronyms

• AC: Action Code (accompanies Transaction Codes like TC 971 or TC 290).
• AMS: Account Management Services (modern web interface for IRS customer service notes and history).
• IDRS: Integrated Data Retrieval System (the command-line mainframe application used for researching taxpayer accounts).
• CNC: Currently Not Collectible (IRS status code indicating taxpayer cannot pay due to hardship).
• CDP: Collection Due Process (formal appeal right given before levy/lien action).
• OIC: Offer in Compromise (agreement between taxpayer and IRS to settle debt for less).
• TAS: Taxpayer Advocate Service (independent organization within the IRS to assist taxpayers facing significant hardship).