Something that's terrific is wonderful, like a terrific concert you'll never forget. Terrific can also describe something very intense, like a terrific thunderstorm.
Anything huge or loud or forceful can be described with the adjective terrific. A marathon runner might put in a terrific effort during the last mile of the race, or a band can make a terrific racket when it practices. Terrific can also mean great, like your terrific new hair cut. Terrific's origin is more scary than wonderful: the Latin root is terrificus, causing terror or fear.