Other forms: propped; props; propping
A prop is something you use as a support, like a broom that serves as a prop to hold a door open. A prop is also something that goes on stage, like a garbage can in a Beckett play.
When you use a prop, you can say you prop something, or prop it up: "Here, prop your blanket fort up with this chair." This handy word also means "a moveable object used on the set of a movie or play." If you get a film job as a prop master, you'll be in charge of placing props in the correct spot before a scene is shot. This theatrical meaning is actually a shortened form of properties.