(deyim) 1. running at or providing maximum power or capacity. 2. a.) so as to make a direct or significant impact. b.) not diluted in nature or effect: "hours of full-on fun"
Full-on is used to describe things or activities that have all the characteristics of their type, or are done in the strongest or most extreme way possible. What they were really good at was full-on rock'n'roll. extreme