The term PART OF IRS refers to three different entities: REVENUE (7 letters), INTERNAL (8 letters), and INT (3 letters). The INTERNAL REVENUE Service (IRS) is a federal agency responsible for collecting taxes and enforcing tax laws. REVENUE is the income generated by the IRS from taxes, fees, and other sources. INTERNAL is the INTERNAL operations of the IRS, such as its organizational structure, policies, and procedures. INT is the INTERNAL Tax Division, which is responsible for administering and enforcing the INTERNAL REVENUE Code.