Plain English Meaning
When ATC tells you to do something, you say it back to them word-for-word so both sides know you heard it right.
Full Definition
The pilot's verbatim repetition of an air traffic control clearance or instruction back to the controller, used to confirm that the message was received and understood correctly. Certain items — such as runway assignments, altitude assignments, altimeter settings, vectors, and hold short instructions — must be read back per FAA procedures.
Context Anchor
Used during radio communication with , especially when receiving an , , , , runway instruction, or instruction.