short for "Steam Lung Therapy" - when you have to stand in a very hot shower for 40 minutes because you smoke too much weed and can't breathe when you wake up.
its short for -stuff like that, shit like that. Because its overused by many people. They don't know what to say so, they say "stuff like that" over and over and over and over. So when they say it over and over you can nick name them SLT.