Plain English Meaning

A piece of restricted airspace that is shared. When the military isn't using it, air traffic control can let other aircraft fly through. When the military is using it, no one else gets in.

Full Definition

Restricted airspace whose using agency (typically the military) has agreed that, when the airspace is not needed for its restricted activity, the controlling ATC facility may release it for use by non-participating aircraft. When released, IFR and VFR traffic may be cleared through it; when active, access is denied or tightly controlled.

Context Anchor

Seen when reading about special use airspace, flight planning, and air traffic control clearances near restricted areas.