To describe someone as a "rock star" is to say that they are exceptionally skilled or talented in their field, and are widely admired for it. The term comes from the world of music, where it refers to a famous singer or musician who has achieved great success and fame. To call someone a rock star is therefore a high compliment, indicating that they have reached the top of their profession through hard work and dedication, and are recognized as an outstanding performer by both their peers and the public at large.