Hellaflush simply means having the wheel Flush with the fenders. This is usually achieved with wheel offset or spacers and usually requirers a good deal of negative camber.
This is a style that is growing at a very rapid pace. It originated from drift cars that were low and had wide wheels pushed out as far as possible. It is also very popular with VIP styled cars as well.
The term "Hellaflush" was coined by Fatlace, and is now one of their brands and the name of their most popular string of car shows. it seams they are slowly leaning toward "Slammed Society" for a brand name. But Hellaflush is here to stay.