A decoupled platform — a term that best describes Core dna — is a headless platform, and then some.
With a decoupled platform, your content and other objects like products, orders, blogs are managed separately and can be front-end agnostic, just like a headless platform. Yet, it has front-end delivery tools in the box, like templates, an admin for your staff and other features that can make adopting the platform easier than if it were just a headless platform. These additional tools are designed for people who don't have technical expertise and can simplify your development process.
The difference is that the back-end and front-end are not “coupled” to each other through a database like with a traditional CMS. Instead, the front-end and back-end communicate to each other through calls to an API.
Learn more about headless content management.