Technically there are internal and external product audits. External audits are not normally described as audits, but they can be called audits. Especially in service companies.
A product audit is an assessment of the final product or service and it s fitness for use evaluated against the intent of the purpose of the product or service. I.e.: Does it meet requirements?
May be performed by:
One of your customers.
Also see 7.4.3 in ISO 9001:2000, and 4.6.4 in QS-9000 (now IATF 16949) .
Internally as a Dock Audit (QS-9000 (now IATF 16949) requirement).
Internally as Final Inspection .
External product audits are typically oriented to a specific customer.
In military manufacturing this used to be called Source Inspection .
ISO 19011 - Quality and Environmental Management Systems Auditing Forum Discussions