The term "subject matter" refers to the content or topic being discussed, analyzed, or studied. It is the main focus and central theme of a particular discussion, conversation, or written work. In essence, it is what the discussion is all about.
It's an honest take on the dark subject matter of alcoholism. (waytooindie.com)
In need of subject matter experts for your story? (prnewswire.com)
The third series, infinite storage, is united by a recurring motif of black holes found in subject matter as diverse as melted fabric to the back of someone's head. (fadmagazine.com)