Tapeworms are a type of parasite, also known as a cestode, which lives in the intestines of infected mammals. Cats may become infected with tapeworms if they eat animal meat that is contaminated with the worms, but in most cases they become infected with tapeworms by ingesting fleas that are carrying tapeworm eggs. Tapeworms are named so because of their long, flattened, shape which looks similar to a piece of tape.