Plain English Meaning

At slower speeds, air behaves as if it cannot be squeezed — its density stays roughly the same as it flows around the airplane. This makes the math and the aerodynamic behavior much simpler.

Full Definition

In aerodynamics, a flow condition in which changes in pressure produce no significant change in the density of the air. Airflow is treated as incompressible at low subsonic speeds (generally below about Mach 0.3), where density variations are small enough to be ignored in calculations of lift, drag, and pressure.

Context Anchor

Used in high-speed flight discussions when comparing ordinary lower-speed airflow with airflow near the speed of sound, where air compression starts to .