Plain English Meaning

The middle part of a flight — after you've finished climbing away from your departure airport and before you start coming down toward your destination. It's the cruise portion, when you're flying along your planned route at altitude.

Full Definition

The phase of flight that begins after departure and climb-out has been completed and ends before the descent and approach phase begins. During the enroute phase, the aircraft is typically established at a cruising altitude and is navigating between waypoints, navaids, or fixes along an established route or .