LiveActor is a class that represents an actor in a scene1). This can be an enemy, level geometry, or anything in between. Most inherited classes use the Nerve system to distribute code to different functions, instead of just 1 update function.
If a LiveActor is “clipped”, its code is not being run and it is essentially being ignored. Whether or not a LiveActor is clipped is managed by the scene it is in, usually its archive gives the scene a clipping radius which determines how far the LiveActor can be from the camera before it is clipped, to save on performance.