As a noun quartet
is (music) a music composition in four parts, each performed by a single voice or instrument.
As a symbol res is
(music) A music composition in four parts, each performed by a single voice or instrument.
(music) The set of four musicians who perform a piece of music together in four parts.
- A string quartet .
A group of four.
- A quartet of violinists .
* group of four: foursome