Plain English Meaning

ATC is giving you a range of altitudes to work within, from the lowest legal IFR altitude up to the one they named. You can pick where to fly inside that range, change altitude when you want, and start your approach when you arrive — all without asking again. The catch: once you leave an altitude and tell ATC, you can't go back to it without permission.

Full Definition

An ATC clearance, issued using the word 'cruise,' that authorizes a pilot to fly at any altitude from the minimum IFR altitude up to and including the altitude specified in the clearance. The pilot may level off at any intermediate altitude within this block, and may climb or descend within it without further ATC authorization. However, once the pilot reports leaving an altitude, that altitude may not be returned to without a new clearance. A cruise clearance also authorizes the pilot to execute an approach at the .