Group piano is the study of how to play the piano in a group setting. This
contrasts with the more common individual/private lesson. Group lesson formats include
master classes, university classes, and pre-college music lessons. These
classes typically have between 3 and 16 students. Benefits of the group
lesson format include the development of independent learning, ensemble
playing, critical listening skills, and exposure to a wide range of
repertoire.
Read more on Wikipedia