Complex sentence: Equivariant maps generalize the concept of invariants, functions whose value is unchanged by a symmetry transformation of their argument, and the value of an equivariant map is often (incorrectly) called an invariant.
Split into simpler sentences: Equivariant maps generalize the concept of invariants, functions whose value is unchanged by a symmetry transformation of their argument. The value of an equivariant map is often (incorrectly) called an invariant.