That isn't a dumb question! It's a weird term... A benched show is one where where all dogs are required to stay in an assigned "benching area" for the duration of the show, (except when being exercised, groomed, or exhibited) in order that the public may easily view the exhibits up close and talk to the breeders, owners, and handlers.
At a show that isn't benched, exhibitors can leave once their breed has shown.
Benched shows are cool for the fact that no matter what time you go, you can see all the breeds/dogs entered... Hope that helps!