This field is set to True when the entry isn't truly movie (e.g. for DVD compilations, music concerts, theatrical performances etc.). You can learn more about it our Contribution Bible. As for the API you can use video field in movie discover API method to filter out non-movie entries by using "include_video=false" parameter.

Movie trailers aren't allowed as standalone records and must be added in the dedicated Videos section of the movie and TV show entries (e.g. here). In the API associated videos are then returned as an array object by videos API method or by generic movie details method when additional parameter "append_to_response=videos" is used.