Plain English Meaning
A licensed pilot who is trained and authorized to teach others how to fly and to sign them off for tests and certificates.
Full Definition
A pilot who holds an FAA Flight Instructor Certificate authorizing them to provide flight and ground instruction to student pilots and other pilots seeking certificates, ratings, or recurrent training. The certificate is issued with specific category and class ratings (such as airplane single-engine, airplane multi-engine, or instrument) that define what the instructor is permitted to teach.
Context Anchor
You will encounter this term throughout pilot training, especially when discussing lessons, , approval, and for pilot tests.