Bulgarian bowed, stringed musical instrument of the Balkans, with a round wooden back, a skin belly, and one horsehair string (or, rarely, two) secured at the top of the neck by a rear tuning peg. It is played in a vertical position, with a deeply curved bow. It has no fingerboard, the string being stopped by the sideways pressure of the player's fingers. It is related to the medieval rebec and the Greek lira and is used in the Balkans to accompany the performance of the guslari, or epic singers.

The word gusla sometimes refers also to the gadulka, a similar Bulgarian instrument with three or four strings. The Russian gusli, an unrelated instrument, is a psaltery.