This tag is used for any sort of "mixed beast," where the body is distinctly made up of parts from a number of different animals.
For example, a wolf with a shark tail and fin. A crocodile with hooves. A fox with wings.
The original Chimera was a creature out of Greek mythology, made up of a combination of lion, goat and serpent. Creatures that match up to this idea should be tagged chimera (mythology).