Self-closing describes a gate that returns to closed without anyone touching it. The action is provided by spring-loaded hinges (light gates), hydraulic hinges (medium gates), or a separate hydraulic gate closer (heavy gates).
AS1926.1 requires every pool-barrier gate to be self-closing from any open position back to fully latched, with no manual help. The gate must return to closed even from the half-open position that a child might leave it in.
Tension setting matters. Too light and the gate doesn't gather enough momentum to engage the latch. Too heavy and the gate slams shut hard enough to be a finger hazard. The Goldilocks closing time is 2 to 4 seconds from fully open to fully closed.