This is a term used in America to describe rockabilly that has been influenced by punk and/or heavy metal. It is normally exemplified by The Reverend Horton Heat and The Cramps. The term is kinda loose and could mean other things depending on where ya are and who you are talking to.
Especially if you are talking to Europeans. They have some narrow definition of the term that seems to exclude every band that's not The Meteors. Those damn European Bastards