A method of "dancing" to grunge and other muddier punk and metal, it involves the entire crowd pushing against each other whilst jumping, rather than moshing where only a few individuals participate. It is more powerful than a mosh because its hard to leave and if one person falls they can drag a large section of the crowd with them.
However there is less actual violence in a slam dancing crowd, and the occasional meathead in one can ruin it for eveyone.
Skanking in a mosh is either being way too confident for your own good or suidical.
"Dude there is a sign on the door of the club saying 'no moshing' that blows."
"so what man, get a bunch of people together and start slam dancing"