The term 'Thimblerig Prop' is a three-letter acronym for PEA, which stands for 'Pick, Exchange, and Admire'. It is a game of chance that was popular in the 19th century. The game involves two players who each have a thimble with a PEA hidden underneath. The players take turns picking up the thimbles and exchanging them, then they both guess which thimble contains the PEA. The player who guesses correctly wins the game.