in theatrical slang, means properties, of which it is a contraction. Everything stored in a theatre for general use on the stage is a “prop,” but these stores are the manager's props. An actor's “props” are the clothing and other articles which he provides for his own use on the stage. In many good theatres the manager provides everything but tights and a few minor articles; but in minor theatres each actor must provide a wardrobe and properties.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894