Damage is any change in a thing, often a physical object, that degrades it away from its initial state. It can broadly be defined as "changes introduced into a system that adversely affect its current or future performance".[1] Damage "does not necessarily imply total loss of system functionality, but rather that the system is no longer operating in its optimal manner".[1] Damage to physical objects is "the progressive physical process by which they break",[2]: 1. and includes mechanical stress that weakens a structure, even if this is not visible.[2]: ix.