Bait

Bait refers any item that can be used for Fishing. If you do not have any bait, you can use the Fishing Pole, but you will be unable to catch fish. Most critters that are insects or mollusks work as bait. If Truffle Worms are used as bait in the ocean it will summon Duke Fishron. However, Truffle Worms cannot be used to catch anything else. Various types of bait are obtainable through use of the Bug Net. A piece of bait has a chance be used whenever you catch somthing, be it a fish or junk, the chance of it being used up is dependant on its bait power(exception being the Truffle Worm). You can get the three non-critter baits by completing a quest for the Angler NPC.

Trivia

 * Master Bait is most likely a play on words which refers to the act of sexual self-stimulation.