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, except for when the group is playing well-known jazz standards or covers of existing popular songs. 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. Jam sessions may be based upon existing songs or forms, may be loosely based on an agreed chord progression or chart suggested by one participant, or may be wholly improvisational. Jam sessions can range from very loose gatherings of amateurs to evenings where a jam session coordinator or host acts as a "gatekeeper" so that appropriate-level performers take the stage to sophisticated improvised recording sessions by professionals which are intended to be broadcast live on radio or TV or edited and released to the public.