Totem is the representation of a symbol by an animal, and totemism is the system or science of such symbolism. Thus, in Egyptian mythology, what is represented as a pig or hippopotamus by one tribe, is (for some totemic reason) represented as a crocodile by another.
“The apparent wealth of [Egyptian] mythology depends on the totemism
of the inhabitants of the Nile Valley. ... Each district had its own
special animal as the emblem of the tribe dwelling in that locality.” —
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894