Plain English Meaning

Points on the approach where you are allowed to come down to a new, lower altitude — but only once you have passed the point.

Full Definition

Waypoints along an instrument approach or arrival procedure that mark points where the aircraft is permitted to descend to a lower published altitude after passing them. Each step down waypoint has its own minimum crossing altitude, and the aircraft must be at or above that altitude until the waypoint is crossed.

Context Anchor

Seen on instrument approach charts and in procedure records for approaches that descend toward the runway in stages.

Derivation

Called 'step down' because the resembles a staircase — the aircraft levels at one altitude, then 'steps down' to the next once past the waypoint.