Fish Tape

Fish tape is a industry term (or slang) to refer to a tool used to get cables through conduit (thin, metal piping about 1" or less in diameter).

Fish tape is a self-contained reel of rigid metal tape.  It's a thin, flat piece of metal about 1/4" wide.

conduit pipes coming out of the ceiling into a network closet (above)

Below is a picture of a reel of 120' of metal fish tape.  You can get fiberglass Fish tape too.