Animation in general goes back to something as simple as the stick figures you may have drawn on your notebook - flip the pages and view your animation. Studios like Disney pioneered 2D animation with it's beautiful hand painted (rendered) scenes and characters. 3D is where animation has evolved to, with and entirely different process and a completely different quality yet the delivery is still the same - as frame by frame video.
Creating an animation in 3D involves setting up a scene complete with everything inside of it. This may include furniture, people and other features. Then the animated parts are added, which in the case of virtual tours is normally just the camera itself. The animation may extend to characters, doors, the wind, cars and practically any other kind of object. Each animation is really an instruction to an object to do something or move somewhere/somehow over a period of time.
A simple example of an animated 3D camera is to instruct it that at 0 seconds be at point 'A' then at 5 seconds be at point 'B'. The computer interpolates everything in between and generates a series of frames that show every point within a split second over that 5 seconds. To take it further you might want to animated a door along the way by telling it that at 2 seconds it is to rotate 90 degrees (open) over a period of 1.5 seconds.
The two simple examples above are nothing compared to character animation! Moving 3D people in lifelike ways is a challenge for only the best 3D animators.