Plain English Meaning
The period right before you start coming down from cruise altitude, when you get everything ready for the arrival and landing.
Full Definition
The phase of flight that occurs after cruise but before the aircraft begins its descent toward the destination airport, during which the pilot prepares for arrival by reviewing weather, briefing the approach, setting up navigation and communication equipment, and planning the descent profile.
Context Anchor
Seen in risk-management and workflow discussions, especially when a pauses before descent to the and plan the next phase of flight.