Prop has two main meanings that come up frequently:

1. A physical object used in a play, movie, or performance to make it more realistic or interesting. When actors perform on stage, they use props like fake swords, telephones, books, or dishes to help tell the story. A wizard's wand in a school play is a prop. So is the steering wheel in a car during a movie scene. The props department in a theater or film studio creates and manages all these objects. Props help audiences believe in the world of the story, even though they know it's pretend.
2. To hold something up or support it so it doesn't fall. You might prop open a heavy door with a doorstop, or prop yourself up against a wall when you're tired. A farmer might prop up a young tree with stakes until its roots grow strong enough to support it alone. When you prop your feet up on a footstool after a long day, you're resting them on something that holds them in a comfortable position.

Both meanings share the idea of providing support: physical props support a story, while propping something up provides physical support.