Failure

The event, or inoperable state, in which any item or part of an item does not, or would not, perform as previously specified.

Hard Failure

A product under test ceases to work correctly. It does not resume correct operation, even when the stressing environment is eased.

Soft Failure

A product under test ceases to operate correctly, but resumes correct operation when the stressing environment is eased.

See also: Failure Mode and Effects Analysis.