Anti-access and area denial is an operational effect, more precisely, a family of related effects that require different capabilities, operate at different ranges, and impose different burdens on an adversary.
Anti-access operates at the strategic-operational level. It aims to prevent or delay an adversary from entering the theater, raising the cost of transit through chokepoints and corridors until intervention becomes delayed, degraded, or politically unsustainable. In its most expansive form, anti-access also targets the infrastructure from which an adversary would mount operations: the bases, logistics nodes, command facilities, and early warning systems that enable power projection.
Area denial operates at the operational-tactical level. It aims to restrict freedom of maneuver within the theater