The boundary layer is an important concept in aerodynamics; its discovery advanced the science of aerodynamics to a useful tool in predicting flows. Today it is an important part of engineering.
Parameters such as boundary layer thickness, displacement thickness, and momentum thickness characterize the boundary layer's size and shape.
The boundary layer equations provide a significant simplification to the Navier-Stokes equations, in two ways: by allowing inviscid solutions to be used outside the boundary layer, and by changing the equations from elliptic to parabolic inside the boundary layer. The equations are valid for high Reynolds number flows, but not when close to the leading edge of the wall.