Which ATC term indicates that an aircraft is about to reach a specific point?

The correct term indicating that an aircraft is about to reach a specific point is commonly referred to as "RR." In the context of air traffic control communications, "RR" signals that an aircraft is preparing to reach and report on a specific fix or point in their flight path. This term is part of standard phraseology used by air traffic controllers to ensure clear and concise communication about the aircraft's progress along its route, which aids in maintaining safe distances between aircraft and managing air traffic efficiently.

Other terms provided do not represent this specific indication. While "RX," "RP," and "RA" may have their own meanings or uses within the realm of air traffic control, they do not apply to the situation of an aircraft approaching a specific waypoint in the same manner as "RR."