is the damage to a solid surface, generally involving the progressive loss of material.  This loss is due to the relative motion between that surface and a contacting surface or substance. These relative motions can be identified in terms of wear contacts of Rolling, Sliding, Spinning or Impaction.  Wear is often confused with other particle or debris generation mechanisms.

	ROLLING	SLIDING
	SPINNING	IMPACTION

Also see abrasion, adhesion, corrosion, erosion, fretting, fatigue and cavitation.