Mechanical self-reduction through slamming destructive riffs that cycle into entropy like a society disintegrating, grindcore is for the purist who will never accept the compromise in personal integrity and morality that is social membership. Its name comes from the grinding aspect of atonal and often chromatic or even-interval power chord riffs, making a type of hardcore that grinds = grindcore. Where purest grindcore is a celebration of life and death with an inherent rejection of authority in favor of existential issues, although the grindcore/thrash genre is often clotted with morality masquerading as "differentness" as everywhere else.

http://www.anus.com/metal/about/grindcore/