Semisimple

In mathematics, the term semisimple (sometimes completely reducible) is used in a number of related ways, within different subjects. The common theme is the idea of a decomposition into 'simple' ('irreducible') parts, that fit together in the cleanest way (by direct sum). Briefly, "semisimple = direct sum of simple", or equivalently "completely reducible = direct sum of irreducible".

See also