I think the analogy is to “domain” meaning “the set of valid inputs to a function”. A business domain is the set of entities a particular piece of software is d

I think the analogy is to “domain” meaning “the set of valid inputs to a function”. A business domain is the set of entities a particular piece of software is designed to work with. It’s a fuzzy “philosophical” term, but it’s not useless and paying attention to these seemingly arbitrary concepts makes a system much nicer to work in.