Plain English Meaning

The way the airplane is set up when it is flying along steadily at altitude — gear up, flaps up, engine set for normal cruising power, and trimmed so it flies level on its own.

Full Definition

The arrangement of an airplane's controls and components used for normal level flight between climb and descent, typically with the landing gear retracted (if retractable), flaps up, propeller and engine settings adjusted for efficient cruise power, and the airplane trimmed for hands-off straight-and-level flight at the chosen airspeed and altitude.