Boundary Layer - F1 Technical Terms

The Boundary Layer is the layer of air in closest contact to the bodywork, as the air moves over the body the air closest to the body sticks to the surface slowing the airflow (Building up the Boundary Layer), as the build up continues to occur along the surfaces length the airflow becomes turbulent and separation occurs. 

Turbulence is an undesired characteristic as with this comes drag and moreover it can impact the efficiency of not only that area of the car but the airflow up and downstream of it.

There are means in which to reduce Boundary Layer build up but in Formula One the only practical way is through the use of Vortex Generators.