This page is a glossary of terms in invariant theory. For descriptions of particular invariant rings, see invariants of a binary form, symmetric polynomials. For geometric terms used in invariant theory see the glossary of classical algebraic geometry. Definitions of many terms used in invariant theory can be found in (Sylvester 1853), (Cayley 1860), (Burnside & Panton 1881), (Salmon 1885), (Elliott 1895), (Grace & Young 1903), (Glenn 1915), (Dolgachev 2012), and the index to the fourth volume of Sylvester's collected works includes many of the terms invented by him.