As used in this part:

(a) Agency means each of the executive agencies and military departments (as defined in 5 U.S.C. 105 and 102, respectively) and the United States Postal Service; and in addition, for city or county withholding purposes only, all elements of the judicial branch.

(b) City means any unit of general local government.

(1) Which:

(A) Is classified as a municipality by the United States Bureau of the Census, or

(B) Is a town or township which, in the determination of the Secretary of the Treasury,

(i) Possesses powers and performs functions comparable to those associated with municipalities,

(ii) Is closely settled, and

(iii) Contains within its boundaries no incorporated places as defined by the United States Bureau of the Census; and

(2) Within the political boundaries of which five hundred or more persons are regularly employed by all agencies of the Federal Government.

(c) City income or employment taxes means any form of tax for which, under a city ordinance:

(1) Collection is provided by imposing on employers generally the duty of withholding sums from the pay of employees and making returns of the sums to a designated city officer, department, or instrumentality; and

(2) The duty to withhold generally is imposed on the payment of compensation earned within the jurisdiction of the city in the case of employees whose regular place of employment is within such jurisdiction. Whether the tax is described as an income, wage, payroll, earnings, occupational license, or otherwise, is immaterial.

(d) Compensation as applied to employees of an agency and members of the Armed Forces means wages as defined in 26 U.S.C. 3401(a) and regulations issued thereunder.

(e) County means any unit of local general Government which is classified as a county by the Bureau of the Census and within the political boundaries of which 500 or more persons are regularly employed by all agencies of the Federal Government.

(f) County income or employment taxes means any form of tax for which, under a county ordinance:

(1) Collection is provided by imposing on employers generally the duty of withholding sums from the pay of employees and making returns of the sums to a designated county officer, department, or instrumentality; and

(2) The duty to withhold generally is imposed on the payment of compensation earned within the jurisdiction of the country in the case of employees whose regular place of employment is within such jurisdiction. Whether the tax is described as an income, wage, payroll, earnings, occupational license, or otherwise, is immaterial.

(g) District of Columbia income tax means the income tax imposed under 47 District of Columbia Code, chapter 15, subchapter II.

(h)(1) Employees for the purpose of State income tax withholding, means all employees of an agency, other than members of the armed forces. For city and county income or employment tax withholding, it means:

(i) Employees of an agency;

(ii) Members of the National Guard, participating in exercises or performing duty under 32 U.S.C. 502; or

(iii) Members of the Ready Reserve, participating in scheduled drills or training periods, or serving on active duty for training under 10 U.S.C. 270(a).

(2) Employees for purposes of District of Columbia income tax withholding, means employees as defined in 47 District of Columbia Code 1551c(z).

(i) Members of the Armed Forces means (1) individuals in active duty status (as defined in 10 U.S.C. 101(d)(1)) in regular and reserve components of the Army, Navy, Air Force, Marine Corps, and Coast Guard, and (2) members of the National Guard while participating in exercises or performing duty under 32 U.S.C. 502 and members of the Ready Reserve while participating in scheduled drills or training periods or serving on active duty for training under 10 U.S.C. 10147.

(j) Ordinance means an ordinance, order, resolution, or similar instrument which is duly adopted and approved by a city or county in accordance with the constitution and statutes of the state in which it is located and which has the force of law within such city or county.

(k) Regular place of Federal employment means the official duty station, or other place, where an employee actually and normally (i.e. , other than in a travel or temporary duty status) performs services, irrespective of residence.

(l) Secretary means Secretary of the Treasury or his designee.

(m) State means a State, territory, possession, or commonwealth of the United States, or the District of Columbia.

(n) State income tax means any form of tax for which, under a State status:

(1) Collection is provided, either by imposing on employers generally the duty of withholding sums from the compensation of employees and making returns of such sums to the State or by granting to employers generally the authority to withhold sums from the compensation of employees, if any employee voluntarily elects to have such sums withheld; and

(2) The duty to withhold generally is imposed, or the authority to withhold generally is granted, with respect to the compensation of employees who are residents of such State.