master class

Short definition from Wiktionary

Noun

1. 1
   A class, typically in a performing art such as music or drama, in which a teacher listens to and critiques the performance of individual students, one at a time, while the other students observe.
2. 2
   An action or series of actions that serve to demonstrate a person's mastery of a subject.
3. 3
   A brilliant or virtuosic performance.