Irish dance can broadly be divided into social dance and performance dance. Irish social dance can be divided into "céilí" and set dancing. Irish set dances are quadrilles, danced by 4 couples arranged in a square, while céilí dances are danced by varied formations of couples of 2 to 16 people. There are also many stylistic differences between these two forms. Irish social dance is a living tradition, and variations in particular dances are found across the country. In some places dances are deliberately modified and new dances are choreographed. Performance dance is traditionally referred to as stepdance. Irish stepdance, popularised by the show "Riverdance", is notable for its rapid leg movements, with the body and arms being kept largely stationary. The solo stepdance is generally characterised by a controlled but not rigid upper body, straight arms, and quick, precise movements of the feet. The solo dances can either be in "soft shoe" or "hard shoe".