Crusher 4 was the title of a holographic dance lesson devised by Doctor Beverly Crusher.

The program featured the recreation of the studio were Dr. Crusher had her first dancing lesson, including a large mirror and a practice beam. Holographic dance partners were available and music, "Isn't It Romantic?," for example, could be played in the studio.

Dr. Crusher taught Data first how to tap dance and then how to dance properly for the O'Brien wedding with the help of this program. (TNG: "Data's Day")