What is "double stop"

n. (context music stringed instruments English) two notes being played simultaneously

In music, a double stop refers to the technique of playing two notes simultaneously on a bowed stringed instrument such as a violin, a viola, a cello, or a double bass. In performing a double stop, two separate strings are bowed or plucked simultaneously. Although the term itself suggests these strings are to be fingered (stopped), in practice one or both strings may be open.

A triple stop is the same technique applied to three strings; a quadruple stop applies to four strings. Double, triple, and quadruple stopping are collectively known as multiple stopping.

Early extensive examples of the double-stop and string chords appear in Carlo Farina's Capriccio Stravagante from 1627, and in certain of the sonatas of Biagio Marini's op. 8 of 1629.