Part of having effective documentation is using consistent terms. Some terms in the Wiki are used interchangeably, and I could see how that would cause confusion. As an example, ArduCopter, TradHeli, Copter, APM:Copter, etc. all can describe the same firmware/control firmware that makes ardupilot great. Every page seems to describe it differently.
In addition to answering the title of this Topic, what other terms should be used throughout the wiki? I would think that we should be using ArduCopter, ArduPlane, ArduRover, ArduSub, etc consistently when speaking about the firmware and control system. Copters, Planes, Rovers, and Subs would refer generically to the physical devices.
That being said, APM is on the front page of Copter (to my understanding APM is outdated/legacy):