Support moves or support work are any moves by the backline that help support a scene. Support moves are in service either of the game or the base reality.
This includes walk-ons, tag-outs, split scenes, a swinging door, scene painting, cut-to as well as fleshing out the environment by playing animals or inanimate objects, or even an edit.
Other support moves include helping a teammate move through space--appearing weightless.
Teams often discuss what support moves they allow as an ensemble as well as individual content or physical boundaries for their sets prior to a show.