foursome; group of four people
General term for any group or set of four people, such as friends, travelers, or a team.
We went on a trip as a group of four.
That foursome always has lunch together.
Gang of Four
Historical term referring to the Maoist political faction led by Jiang Qing during China's Cultural Revolution. Often used with the definite article in English.
The Gang of Four fell from power at the end of the Cultural Revolution.
Compound of 四 (four) + 人 (person) + 組 (group, set). The historical sense is a direct translation of the English 'Gang of Four'.