What is an "apostate" ...or... an "apostate website?"
If you are an ex-Jehovah's witness and you have publicly or in conversation disagreed with the Watchtower, you are an apostate.
Websites that oppose or criticize the Watchtower are deemed apostate.
However...
To everyday Jehovah's Witnesses anyone (ex-witness or not) displaying too much knowledge of the organization, its workings and who is critical of it is deemed an apostate. Any site that criticizes the organization or its teachings in any way shape or form is apostate (if not a media outlet). If its a mainstream media outlet the article or segment is deemed apostate or Satan inspired.
So although the technical definition is pretty narrow the practical application is pretty broad.