When five people do something together, you can refer to them as a quintet. If only there were that fifth Beatle, then they would have been considered a quintet. Sigh.
The most common kind of quintet is a five-person musical group. A string quintet might be made up of two violinists, a viola player, and two cellists, while your cousin's a cappella quintet will have five harmonizing singers. If you can usually be found hanging out with your four best friends, people might call the five of you a quintet. The original meaning was "musical composition for five voices," from the Latin quintus, "the fifth."and quinque, "five."