Plain English Meaning

A super-thin film of smooth, orderly air sliding along the wing's skin, sitting underneath the rougher, more mixed-up air just above it.

Full Definition

A very thin layer of air flowing smoothly along the surface of an airfoil, located within the larger boundary layer, where the airflow remains in orderly parallel sheets rather than tumbling and mixing. It exists immediately adjacent to the wing surface and is the slowest-moving portion of the boundary layer.

Context Anchor

Seen in aerodynamic discussions of airflow over wings and other aircraft surfaces, especially when explaining boundary layers, drag, and .