Plain English Meaning

The front edge of the wing — the rounded edge that hits the air first when the airplane moves forward.

Full Definition

The forward edge of an airfoil — the part of a wing, propeller blade, or tail surface that meets the oncoming air first as the aircraft moves forward.

Context Anchor

Seen when learning the parts of the wing and tail, during preflight inspection, and when discussing ice, damage, or airflow over the airplane.

Derivation

Leading' here means 'going first' or 'in front.' The leading edge is simply the edge that leads — the one out in front as the wing moves through the air. The opposite is the trailing edge, the edge that trails behind.