Active exercise:

An exercise performed without assistance. A sit-up, for example, is an active exercise.

Passive exercise:

An exercise performed with assistance, usually from a therapist, that requires the exerciser to exert little physical energy. Passive exercises are important during the acute, or early, phase of recovery from an injury.

Resisted exercise:

An exercise performed against resistance. All weight-training exercises, for example, are resisted exercises.