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.

/prɑːp/ -pp- to support something physically, often by leaning it against something else or putting something under it: I propped my bike (up) against the wall.

'Prop' is the short form of proprietary. Prop shops employ a number of trading strategies for assets that range from simple liquid assets such as stocks and bonds to sophisticated instruments such as collateralized debt obligations (CDO), derivatives, and commodity futures.