Any question like this can be answered by going to wikipedia and looking up stoner rock...
But since you asked, stoner rock is rock to get stoned to... Obviously, but... it's usually slow-paced, heavy, somewhat psychadelic, etc. And I'm not a big weed guy, but I've smoked weed and listened to Kyuss, Sabbath, shit like that, and it actually does sound a lot better when high -- though a lot of music does, so...
Anywho:
http://en.wikipedia.org/wiki/Stoner_rock