Definition from Nolo’s Plain-English Law Dictionary
Damage or loss to an item (such as a table) or element of a room (such as the floor) resulting from ordinary use and exposure over time. The term is commonly used in leases to limit the tenant's responsibility to repair damage, repaint the walls, or replace items when moving out. The term is subjective, but more wear and tear can be expected the longer the occupancy or the worse the condition of the premises when the tenant moved in. This is often a source of conflict between landlord and tenant, particularly when there is a deposit for any damages beyond reasonable (sometimes called normal or ordinary) wear and tear.