Plain English Meaning

How full the air is of moisture compared to how much it could hold right now. 100% means the air is completely full and water will start to condense; 50% means the air is holding half of what it could.

Full Definition

The ratio, expressed as a percentage, of the amount of water vapor actually present in a given volume of air to the maximum amount that air could hold at the same temperature and pressure.

Context Anchor

Seen in weather reports, maintenance conditions, and discussions of moisture, fog, corrosion, and icing .