It's specific jargon in the Domain Driven Design community; "domain" == "business domain". Some of the links in that section of the OP give more detail. I reco

It's specific jargon in the Domain Driven Design community; "domain" == "business domain". Some of the links in that section of the OP give more detail. I recommend DDD in particular, it's a great architectural framework, though it's a bit dense and hard to approach. A good starting point: https://martinfowler.com/bliki/DomainDrivenDesign.html https://martinfowler.com/bliki/DomainDrivenDesign.html