Beach music, also known as Carolina beach music, and to a lesser extent, Beach pop, is a regional genre which developed from various rock/R&B/pop music of the 1950s and 1960s. Beach music is most closely associated with the style of swing dance known as the shag, or the Carolina shag, which is also the official state dance of both North Carolina and South Carolina. Recordings with a 4/4 "blues shuffle" rhythmic structure and moderate-to-fast tempo are the most popular music for the shag, and the vast majority of the music in this genre fits that description.