Sources and scope for this page: ISO 3002-1:1982, covering the definition of relief angle. No independent source check is recorded for this page: the content rests on the sources listed and on the working shown on the page. How sources, methods and updates are recorded.
Definition
Relief and clearance mean the same thing, and both terms appear in tooling catalogues. Where catalogues distinguish them, relief is the primary flank angle and clearance is the secondary one, but in most usage they are interchangeable.
The term survives mostly because older British and American texts used "relief" while ISO standardised on "clearance". Seeing both in one document is normal and does not indicate two different features.
Common misuse
Treating relief and clearance as different features and specifying both, which produces a contradictory tool drawing.