Drum circles originated in the United States during the late 1960s and early 1970s for any group of people, particularly counterculture groups, who gather (informally) to play music together. The terms "drum jam" or "jam session" could be substituted. Settings include beaches, parks, concert parking lots, festivals, and retreats. The determining criteria for a drum circle are that the music is improvised and co-created by the participants. Drum circles may or may not be open to the public, but the music is always a group expression, not constrained by genre, instrumentation, or directed by one person or sub-group.