Real Dictionary

string quartet
countable noun: A string quartet is a group of four musicians who play stringed instruments together. The instruments are two violins, a viola, and a cello.

string quartet in American English
a quartet of players on stringed instruments, usually first and second violins, a viola, and a violoncello
noun: a musical composition, usually in three or four movements, for four stringed instruments, typically two violins, viola, and cello

string quartet in British English
noun: an instrumental ensemble consisting of two violins, one viola, and one cello