An illegal substance (Marijuana) that is inhaled through a pipe, and the resulting effect is fucking insane. IT makes you feel all floaty n' shit. It messes with your nervous system or some shit cause it is really crazy, and probably laced with meth and cocaine. Also maybe heroin. But it is DEFINITELY worth the title of "Space Weed".
George: (tweakin out on the floor) I feel so right man. So right...
Tim: Yeah dude it's fuckin' space weed.