Correct keyword for TV Series Movie

Yes, I understand that keyword applies. What I'm trying to determine is which keyword is appropriate, and more specific, when it is not just based, but more like a long-form episode, or exceptional adventure. For example, Star Trek (2009) vs Star Trek: First Contact (1996). Both are based on a TV series, but not in the same way. Would you agree the nature in which they are based on the TV series is different? I'm trying to find a proper keyword to further describe that. In Star Trek (2009) you get introduced to the characters, you need no previous knowledge of the TV shows at all. Whereas Star Trek: First Contact (1996) might be enjoyable for someone with absolutely no knowledge of any Star Trek series, if it very much more connected to TNG. Same actors, etc. With a lower budget or without such cultural presence as ST has, it could have been a "tv movie". But when that doesn't apply, what is it? What keyword sets it apart when, in a way that I lack the words to describe, in essence, it is the TV series?