If we are to be technical about this then a “String quartet, is a musical composition for two violins, viola, and cello in several (usually four) movements. It has been the predominant genre of chamber music since about 1750.” according to the Encyclopedia Britannica. Possibly the most famous contemporary string quartet is the Vitamin String Quartet. They record covers of pop music. My own personal favourite would be their cover of ‘Somewhere Only We Know” by Keane. Have a listen!