Traditionally transit hotel referred to accommodation airside and airport hotel referred to accommodation outside the terminal but usually on airport property.
As is often the case, with time usage changes and hotel marketers abuse terms they feel will be in their favor.
So now you frequently see the term “airport hotel” applied to properties within a few miles of the airport (sometimes even further if they provide airport shuttles). And some on airport property hotels present themselves as “transit hotels” since their guests are often transiting, not staying in the country (but obviously ‘entering’ the country since they cleared immigration to reach the hotel).
If you talk with experienced travelers, your terms will be understood as you expect them too. If you talk with casual travelers or new travelers, their understanding maybe different.