Plain English Meaning
It is the paperwork a pilot fills in when they want the FAA to issue them a new certificate or add a new rating to the one they already hold. The instructor signs it to show the applicant is ready, and the examiner uses it on the day of the checkride.
Full Definition
The official FAA application form (FAA Form 8710-1) used by an applicant to apply for a pilot certificate or to add a rating to an existing certificate. It records the applicant's personal information, pilot experience, training history, and the certificate or rating being sought, and is reviewed and signed by the recommending instructor and the examiner conducting the practical test.
Context Anchor
Seen during practical test preparation, instructor recommendations, IACRA submissions, and FAA checkride paperwork.