The Act's major provisions impose certain requirements and prohibitions on every “employer” subject to their terms. The employment by an “employer” of an “employee” is, to the extent specified in the Act, made subject to minimum wage and overtime pay requirements and to prohibitions against the employment of oppressive child labor. The Act provides its own definitions of “employer”, “employee”, and “employ”, under which “economic reality” rather than “technical concepts” determines whether there is employment subject to its terms (Goldberg v. Whitaker House Cooperative, 366 U.S. 28; United States v. Silk, 331 U.S. 704; Rutherford Food Corp. v. McComb, 331 U.S. 772). An “employer”, as defined in section 3(d) of the Act, “includes any person acting directly or indirectly in the interest of an employer in relation to an employee but shall not include the United States or any State or political subdivision of a State, or any labor organization (other than when acting as an employer), or anyone acting in the capacity of officer or agent of such labor organization”. An “employee”, as defined in section 3(e) of the Act, “includes any individual employed by an employer”, and “employ”, as used in the Act, is defined in section 3(g) to include “to suffer or permit to work”. It should be noted, as explained in part 791 of this chapter, dealing with joint employment, that in appropriate circumstances two or more employers may be jointly responsible for compliance with the statutory requirements applicable to employment of a particular employee. It should also be noted that “employer”, “enterprise”, and “establishment” are not synonymous terms, as used in the Act. An employer may have an enterprise with more than one establishment, or he may have more than one enterprise, in which he employs employees within the meaning of the Act. Also, there may be different employers who employ employees in a particular establishment or enterprise.