A quartet refers to a group of four musicians who play any given style of music. The type of quartet is denoted in the first word, such as "string," which describes the kind of instrument involved.
Many composers exist who have created numerous works for string quartets. The most famous notables are Joseph Haydn, Mozart and Antonio Vivaldi. These renowned composers started writing this genre in the eighteenth century.
Two violins exist in this setting for an important reason. The "Los Angeles Times" website states that the first violin is the foremost instrument and plays the main melody of the piece. The second violin backs up the first and usually accompanies with softer dynamics.