A Domain may be made up of one or more Models

Each business tends to have one core problem it intends to solve. But for the product to be useful and valuable to users, many other supporting aspects have to be put in place.

For example, a Banking application's core value is in providing Accounting Services. But it needs to ensure only authorized users can access an account's details. So Security and Authentication, though a separate concern, is a very important area without which the banking application will not be able to deliver value.

In reality, most products deal with more than one core area in their functionality. Most business problems hold two or more of such supporting areas, called Subdomains within them.

Each such subdomain has a clear boundary, represented as Bounded Contexts in software. Such Bounded Contexts encapsulate Architecture Patterns within themselves.