Your innards are your stomach, intestines, and other abdominal organs. Catching a fish is fun, but gutting it, or removing its innards, is less fun.
The slang term innards is sometimes used to mean "the parts of the digestive system," and other times refers more generally to any of the inside parts or organs of a human or animal body. Innards was coined in the 1800s, originally spelled innerds, from a dialect form of inwards, and meaning "the bowels."