Jam session

A jam session is a relatively informal musical event, process, or activity where musicians, typically instrumentalists, play improvised solos and vamp over tunes, drones, songs, and chord progressions. To "jam" is to improvise music without extensive preparation or predefined arrangements. Original jam sessions, also called "free flow sessions," are often used by musicians to develop new material (music) and find suitable arrangements. Both styles can be used simply as a social gathering and communal practice session.