What is a predetermined geographical position used for route definition and/or progress reporting called?

A predetermined geographical position used for route definition and/or progress reporting is referred to as a waypoint. Waypoints serve as specific locations in navigation that pilots and air traffic controllers use to aid in flight planning, tracking, and reporting. These points can be established by various means, including GPS coordinates or designated visual landmarks, and they help create structured flight paths within controlled airspace.

Waypoints are essential for both en-route navigation and for determining when to report a flight’s position to air traffic control. They facilitate easier communication and coordination within the busy airspace, as pilots can refer to these standardized points when providing updates on their location.

Other terms like "check point," "reference point," and "navigation point" might imply similar concepts, but they do not specifically designate the same significance that waypoints hold in aviation. The term "waypoint" has a clear and recognized function in navigation, making it the most appropriate choice in this context.