When used in this chapter, and for the purposes of this chapter—

(a) A case shall be held to involve or to grow out of a labor dispute when the case involves persons who are engaged in the same industry, trade, craft, or occupation; or have direct or indirect interests therein; or who are employees of the same employer; or who are members of the same or an affiliated organization of employers or employees; whether such dispute is (1) between one or more employers or associations of employers and one or more employees or associations of employees; (2) between one or more employers or associations of employers and one or more employers or associations of employers; or (3) between one or more employees or associations of employees and one or more employees or associations of employees; or when the case involves any conflicting or competing interests in a "labor dispute" (as defined in this section) of "persons participating or interested" therein (as defined in this section).

(b) A person or association shall be held to be a person participating or interested in a labor dispute if relief is sought against him or it, and if he or it is engaged in the same industry, trade, craft, or occupation in which such dispute occurs, or has a direct or indirect interest therein, or is a member, officer, or agent of any association composed in whole or in part of employers or employees engaged in such industry, trade, craft, or occupation.

(c) The term "labor dispute" includes any controversy concerning terms or conditions of employment, or concerning the association or representation of persons in negotiating, fixing, maintaining, changing, or seeking to arrange terms or conditions of employment, regardless of whether or not the disputants stand in the proximate relation of employer and employee.

(d) The term "court of the United States" means any court of the United States whose jurisdiction has been or may be conferred or defined or limited by Act of Congress, including the courts of the District of Columbia.