From Wikipedia... really

“Crossover thrash … is a fusion genre of thrash metal and hardcore punk. The genre lies on a continuum between heavy metal and hardcore punk. Other genres … such as metalcore and grindcore, may overlap with crossover thrash. The genre is often confused with thrashcore, which is essentially faster hardcore punk rather than a more punk-oriented form of metal… The "-core" suffix of "thrashcore" is sometimes used to distinguish it from crossover thrash and thrash metal, the latter of which is often referred to simply as "thrash", which in turn is rarely used to refer to crossover thrash or thrashcore.”