Plain English Meaning
The side that the wind blows toward after passing over something. If wind hits a hill, the leeward side is the back side — where the air tumbles down and gets choppy.
Full Definition
The side of an obstruction, terrain feature, or structure that is sheltered from the wind — the downwind side. Air flowing over the obstruction descends and becomes turbulent on this side, often producing rolling, swirling currents and downdrafts that can extend well beyond the obstruction itself.
Context Anchor
Seen in weather, mountain flying, and discussions of wind flowing around buildings, trees, ridges, or other obstructions.
Derivation
From the Old English 'hleo,' meaning shelter or protection. The 'lee' of something is the sheltered side — out of the wind. In aviation, that sheltered side is also where descending, collects, so 'sheltered' does not mean '.'