maximal torus
Let be a compact group, and let be an element whose centralizer has minimal dimension
(such elements are dense in ). Let be the centralizer of . This subgroup
is closed since where is the map , and abelian
since it is the intersection of with the Cartan subgroup of its complexification, and hence a torus, since (and thus ) is compact. We call a maximal torus of .
This term is also applied to the corresponding maximal abelian subgroup of a complex semisimple group, which is an algebraic torus.