Adj- Describing anything that is of particular or noteworthy greatness. Traditionally used by the youth subculture. Synonym of "extremely awesome." Derived from the slang words "Sick" and "Ill;" it is the next step in the progression in greatness (Sick-Ill-Terminal)
"Dude! That show was off the hook! It was terminal!"
"Did you see that backflip? That was so terminal!"