Salsa is a dance form with origins from the Cuban Son (circa 1920s) and Afro-Cuban dance (specifically Afro-Cuban Rumba). It is commonly associated with the salsa music style, although it may be danced under other types of music with an 8-count rhythm.
The arms are used by the "lead" dancer to communicate or signal the "follower," either in "open" or "closed" position. The open position requires the two dancers to hold one or both hands, especially for moves that involve turns, putting arms behind the back, or moving around each other, to name a few examples. In the closed position, the leader puts the right hand on the follower's back, while the follower puts the left hand on the leader's shoulder.