Set has several meanings:
1. A Group of Dancers, usually a specific number in a particular formation as in 'square sets' or 'longways sets'
2. A number of tunes played one after the other. Most often three but any number from 2 upwards is known. Usually, the tempo and style is kept the same (e.g. 3 reels or 3 jigs) but the key is altered for interest. Occassionally, the style is changed for the last tune (e.g. 2 jigs and a reel).
3. A dance move in Square Dances such as the Lancers where the couples or corners side chasse right and then left while facing. One hand is typically held high, the other may be at the hip. Usually followed by a pivot or Swing.