Plain English Meaning
A mix-up between what the controller said, what the pilot repeated back, and what the controller heard. Either the pilot repeats it wrong, or the pilot repeats it right but the controller doesn't catch a mistake. Either way, the two end up disagreeing without realising it.
Full Definition
A communication failure between pilot and controller in which an incorrect clearance is either read back inaccurately by the pilot or read back correctly but not caught by the controller when listening to the readback. The result is that pilot and controller end up operating on different understandings of the same clearance.
Context Anchor
Seen in radio communication with air traffic control, especially when receiving altitude, heading, , , or .