What does it mean if a track has 'Soundtracks' genre?

[lololol12321]

API reference: https://developer.spotify.com/documentation/web-api/reference/get-track

I'm using Spotify API to get track genres data for a research project. However, it's not clear to me how this variable is defined, generated (human or machine) or updated over time.

One genre of particular use for me is 'Soundtracks'. I'd like to identify songs that are specifically written for and / or used in movies, tv shows, etc. And I wonder how useful this information would be for identification purposes. Specifically,

1. If a song has 'Soundtracks' genre, does it accurately mean it has been used as a soundtrack in a movie, show, etc.?
2. If it doesn't have this genre, does it necessarily mean that it's never used as a soundtrack somewhere?
3. Is there a way to tell apart songs that are "written" for a movie, from those that are merely "used"/"featured" in it?
4. Is there a way to tell lyricless soundtracks (like original scores) from soundtrack songs that have lyrics? (I do notice that songs with the sole genre of 'soundtracks' are all original scores in a small sample I have but can't infer with confidence that it is the case for all)

I googled it but coudln't find definite answers so I'm trying my luck here. Any comment is appreciated! 🙂 Thank you in advance!