Plain English Meaning
A person the FAA has authorized to act on its behalf for specific aircraft inspection and paperwork tasks, such as approving an aircraft as safe to fly or issuing a one-time permit to ferry an aircraft that doesn't currently meet normal airworthiness requirements.
Full Definition
A private individual appointed by the FAA under 14 CFR 183 to perform certain airworthiness-related functions on the agency's behalf, including the inspection of aircraft and the issuance of airworthiness certificates and special flight permits.
Context Anchor
You may see this term when an aircraft needs a special flight permit, such as approval to fly to a place where maintenance or inspection will be done.