RadAn abbreviation of 'radical'--a term made popular by the Teenage Mutant Ninja Turtles. Still primarily used by people on the West Coast who find words like 'cool', 'awesome', and 'tight' to be tired and overused; 'rad' is generally considered to be a much higher praise than the aforementioned superlatives. Also used as a general expression of awe."Those are some rad shoes.""Oh, RAD."