Quartet

noun

1. A music composition in four parts, each performed by a single voice or instrument.

   "A string quartet."

2. The set of four musicians who perform a piece of music together in four parts.

   "A quartet of violinists."

3. A group of four singers, usually males, who sings together in four-part harmony.

   "A gospel quartet."

4. Any group of four, especially people.