More regulatory jargon here. The correct answer above probably seems a bit circular, in that it essentially says that an amateur station is defined as a station in the amateur radio service. But that's about right. A radio station, generally, is simply any collection of devices that, when used together by a sufficiently trained operator make possible communication via radio. What makes a radio station an "amateur" station, and not some other sort of radio station, is simply the intent of its owner for the station to be used in the amateur radio service, as opposed to some other service.
T1A10: What is the FCC Part 97 definition of an amateur station?
- A station in an Amateur Radio Service consisting of the apparatus necessary for carrying on radio communications
- A building where Amateur Radio receivers, transmitters, and RF power amplifiers are installed
- Any radio station operated by a non-professional
- Any radio station for hobby use
The correct answer is A–A station in an Amateur Radio Service consisting of the apparatus necessary for carrying on radio communications.
Not necessarily every radio owned by an amateur radio operator, or installed at the location of an amateur radio station, will necessarily be part of that amateur's station. For example, my Android phone contains five radios, and yet it is not part of either of my amateur radio stations since currently my Android isn't directly used for radio communication within the amateur service. (Not that it can't be. There are ways I could use my Android in conjunction with other devices to form an amateur radio station. I just haven't yet.)
Also, despite the term, stations need not be stationary. The use of "station" is something of an archaism from the days when radio transmitters were huge and effectively immobile. Modern transmitters can be quite tiny and thus very portable. Amateurs may also have as many stations as they want. Originally we had to declare to the FCC the location of our "primary" station (and hams in many countries still have to do this) and were allowed only one such "primary" station, but the FCC has long since done away with this. US hams may have as many primary fixed stations as they want (including none), and may have as many additional portable and mobile stations as they can afford. The FCC used to require that certain classes of station (auxiliary, repeater, and beacon stations) be separately licensed, but that requirement has also been done away with and any ham (other than a Novice) may operate any number of stations in one of these special operational modes with no special notice to the FCC.