I believe that they've moved away from this terminology, but when Disciplined Agile was newer, the creators described it as a "process decision framework".
DA is centered around high-level activity phases for a project and goals within each phase. These aren't strict phase-gate phases, but rather a way to organize the goals. However, DA doesn't tell you how to go about accomplishing these goals. It's more like a library of practices and information about which ones work well together.
We can take a concrete example of Scrum for more information.
Scrum doesn't tell you how to form your team. DA recognizes that there are choices to be made about where the team members come from, such as repurposing an existing team or creating a new team. There are also different structures such as feature teams and component teams or geographic distribution of the team or the dedication of the team members (full-time, as needed). All of these are decisions that would be considered as part of DA.
Scrum tells you that you need a potentially releasable product Increment after every Sprint. DA recognizes that there are choices to be made about how to go about doing this. Are you going to be using BDD? TDD? Maybe a combination of both? Are you going to produce formal design specifications? Maybe you'll be using mob programming to evolve the design with the whole team. Or maybe you'll build proofs-of-concept and demonstrate those.
There are even higher-level choices. Do you have cadences or do you perform work just-in-time, for example. The same sets of roles, phases, goals, and activities can be used to describe a number of processes. It's been mapped to a Scrum-based lifecycle, a just-in-time Lean lifecycle, and even an exploratory delivery lifecycle. All of these are built using the same building blocks, with just a different set of choices.
Some choices are mutually exclusive. Some combine well.
You could have 5 organizations adopting Disciplined Agile. They would likely be able to communicate with each other using DA's fixed sets of roles, phases, and goals. However, each organization may have a different way of satisfying those goals, so their lifecycle would look entirely different.
DA brings a framework that lets an organization build a process lifecycle that is appropriate for their needs. It's not prescriptive at all, but it guides the organization through the things that need to be thought of along the way and some ideas of common practices that have been known to work.