Contact area

When two objects touch, only a certain portion of their surface areas will be in contact with each other. This area of true contact, most often constitutes only a very small fraction of the apparent or nominal contact area. In relation to two contacting objects, the contact area is the part of the nominal area that consists of atoms of one object in true contact with the atoms of the other object. Because objects are never perfectly flat due to asperities, the actual contact area is usually much less than the contact area apparent on a macroscopic scale. Contact area may depend on the normal force between the two objects due to deformation.

This keyword could refer to multiple things. Here are some suggestions: