Plain English Meaning
How much actual air is packed into a given space. Thicker air has more molecules in it; thinner air has fewer.
Full Definition
The mass of air contained in a given volume, typically expressed in slugs per cubic foot or kilograms per cubic meter. Air density decreases as altitude, temperature, or humidity increases, and increases as pressure rises. It directly affects aerodynamic lift, engine power output, and propeller efficiency.
Context Anchor
Encountered when setting up and evaluating a climb, especially on hot days, at higher-elevation airports, or anytime climb performance is affected.
Derivation
From Latin densus, meaning 'thick' or 'crowded.' literally describes how crowded the air molecules are in a given space — useful because , , and engine all depend on bumping into those molecules to do their .