What is the difference between swing and ensemble?

Question

in play terms, of course :)

Answer 1

Ensemble members have parts that they play every night whereas a swing fills in wherever necessary.  Ensemble members also often understudy principals (for example, in the Phantom of the Opera ensemble members understudy Raoul, Christine, Meg and the Phantom) and then the swings understudy sub-principals (I have a friend who is a swing on Phantom and he understudies Firman, Andre, Reyer and the Auctioneer) and fill in for ensemble members who are playing leads or are off sick.  Swings have to know a lot more parts as they could be any of probably six or eight different ensemble members on a given night.