Plain English Meaning

Air that still has room to hold more moisture before it would start forming clouds or dew. It is not yet 'full' of water vapor.

Full Definition

Air that is holding less water vapor than the maximum amount it could hold at its current temperature. Because it is below its saturation point, its relative humidity is less than 100 percent and no condensation, cloud, or visible moisture is forming from it.

Context Anchor

Seen in weather and atmospheric stability discussions when explaining why rising air may cool without immediately forming clouds.