Plain English Meaning
The active waypoint is the place the navigation system is currently steering you toward. Out of all the points in your route, it is the one you are flying to right now.
Full Definition
In a Flight Management System (FMS) or GPS navigator, the active waypoint is the specific waypoint the aircraft is currently navigating toward. It is the next point in the loaded flight plan that the system is using as its target, and all course, distance, and time-to-go calculations on the navigation display are referenced to it.
Context Anchor
Seen on flight management system and GPS route pages, map displays, and navigation status lines during , , and .