Plain English Meaning
It is the instructor's signed sign-off that says, 'This student is ready for the checkride.' Without it, the student cannot take the test.
Full Definition
A flight instructor's formal endorsement in a student's logbook certifying that the student has received the required training and is prepared to take an FAA practical test (checkride) for a pilot certificate or rating. The recommendation carries regulatory weight: the instructor is attesting that the applicant meets the training and proficiency standards required by 14 CFR Part 61.
Context Anchor
Seen when a flight instructor signs a student’s logbook or application before the Federal Aviation Administration practical test.