In algebra, given an algebraic group G, a G-module M and a G-algebra A, all over a field k, the module of covariants of type M is the A G {\displaystyle A^{G}} -module
where − G {\displaystyle -^{G}} refers to taking the elements fixed by the action of G; thus, A G {\displaystyle A^{G}} is the ring of invariants of A.