Plain English Meaning

It's the spot on a route where the lowest legal altitude changes, so the pilot has to climb (or descend) to the new minimum before going further.

Full Definition

An MEA step is the point along an airway or route where the Minimum En Route Altitude changes from one value to another, requiring the pilot to climb or descend to the new MEA before continuing along the route segment.

Context Anchor

Seen on IFR en route charts and in discussions of route segments where navigation signal coverage or obstacle clearance requires a different minimum altitude.

Derivation

MEA stands for Minimum En Route Altitude. 'Step' is used in the everyday sense of a change — like a step on a staircase — because the altitude requirement steps up or down at that on the route.