Velocity [dynamic] boundary layer

A boundary layer characterized by a large transverse gradient of the axial velocity component which produces transverse momentum transfer.
Comment. Depending on the nature of the fluid flow, we distinguish between a "laminar (velocity) boundary layer" and a "turbulent (velocity) boundary layer." Also used is the term "mixed (velocity) boundary layer," when laminar and turbulent flow regions, separated by a "transition region" in which the flow pattern changes, exist simultaneously along the flow.