Ahhh, the dreaded "/", gotcha. Basicly, you slide your left hand down the neck from an undetermined fret (but somewhere high) and land on the opening chord or note. Kinda like a fake "dive bomb" sound but without using a wammy bar. I've also seen tabs where "/" means a pickscrape down the neck.
You could also try starting from a lower fret,sliding up and then back down.