What term refers to a methodically and thoroughly written discussion of a topic?

The correct answer is "treatise" because it denotes a formal and systematic written work that explores a particular subject in depth. A treatise is characterized by its thoroughness and structured approach, often presenting an argument or a detailed analysis on a specific topic. Unlike an essay, which might explore a topic more subjectively or with a personal perspective, a treatise aims for academic rigor and comprehensiveness.

While an article may present information on a topic, it does so in a concise manner, typically intended for publication in a magazine or journal, often focusing on more current subjects. A report tends to summarize findings from research or investigations rather than provide a deep discussion of a subject. Thus, when seeking a term that embodies a comprehensive and scholarly discussion, "treatise" is the most fitting choice.