Plain English Meaning

The first part of an instrument approach. It begins where the published approach starts (the initial approach fix) and ends where the aircraft is lined up and ready to fly inbound on the intermediate part of the approach. Its job is to get the aircraft pointed roughly the right way and stepped down to a workable altitude.

Full Definition

The segment of an instrument approach procedure between the initial approach fix (IAF) and the intermediate fix (IF) or the point where the aircraft is established on the intermediate course or final approach course. This is where the aircraft transitions from the en route or arrival phase toward the final approach by maneuvering, descending, and aligning with the approach course.