Sorry, but I'm confused by this usage of faculty. Must be a UK vs American English thing. What exactly is "a faculty" in this case? I'd only ever say "the faculty", referring to the teaching staff of a particular institution, and I don't think a department could be "in" this sort of faculty.
I've only really heard it in the context of university, but where I am a faculty is a collection of departments/subjects. So, the Computer Science department would be in the Engineering faculty in the university, for example. I'm not sure what it means by in "a" faculty, as opposed to "the" faculty.
This sentence very much reflects the organisation of UK secondary (high) schools.
If there are only a small number of teachers teaching a subject, eg music, then they would be grouped into a department (adran).
In a broader subject area such as Science, there would be separate departments for each of the sciences, usually Biology, Physics and Chemistry, to organise the teaching of their subjects. They would also be grouped into the Science Faculty (cyfadran) to organise the teaching of the General Science courses.