Definitions for "Boundary layer"
The relatively still layer of water just above the bed of a river.
The relative speed of airflow varies with the distance away from the surface. Right next to the surface there is no measurable relative motion. The thin boundary layer is slowed down by the presence of the surface.
A layer of fluid, close to the surface of a body placed in a moving stream, that is distinguishable from the main airflow by distinctive flow characteristics of its own caused by friction Glossary Index