coefficient of friction

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The ratio of the force of friction between an object and a surface to the frictional force resisting the motion of the object.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun physics The ratio between (1) the magnitude of the force of friction which a surface produces on an object (moving along the surface or being pressed statically against it) and (2) the magnitude of the normal force which is produced by the surface on the object and which is perpendicular to that surface.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the ratio of the weight of an object being moved along a surface and the force that maintains contact between the object and the surface