The act of rubbing the surface of one body against that of another; attrition. Many bodies by friction emit light, and friction generates or evolves heat.

In mechanics, the effect of rubbing, or the resistance which a moving body meets with from the surface on which it moves.

In medicine, the rubbing of the body with the hand, or with a brush, flannel; or the rubbing of a diseased part with oil, unguent or other medicament.