The Definition of Done is a formal description of the state of the Increment when it meets the quality measures required for the product. It is the Increment's commitment, an explicit standard the work must reach before anyone calls it finished, and its job is to make "done" mean the same thing to everyone on the team, on every item, every time.
Why it is a commitment rather than a checklist
Framing it as a commitment rather than a process artifact is the 2020 Guide being precise. A checklist is something you tick, while a commitment is something the Increment has to satisfy before it exists at all. An item that misses it does not become a smaller Increment, it goes back to the Product Backlog.
The practical difference shows in what the standard is allowed to bend for. A checklist can be waived when a release is urgent and a commitment cannot, because once quality is negotiable item by item, the word Done carries no information and every forecast resting on it is guesswork.
The transparency it creates
The standard exists so that everyone shares an understanding of what work was actually completed. Without it the Developers know what they built and nobody else can tell what a finished item means, so the Product Owner cannot judge whether an item is releasable and stakeholders cannot tell what they are looking at.
That is also what makes counting possible. If Done is one standard, the number of items meeting it measures real progress toward the Product Goal. If Done varies by item and by week, forecasts and release dates are calculated from a figure that means nothing.
Work that misses it returns to the Product Backlog
An item that does not meet the Definition of Done cannot be released or even presented at the Sprint Review. It returns to the Product Backlog for future consideration, where it competes with everything else for order rather than waiting in a private queue of nearly finished work.
That last part is where people stop reading. Returning an item does not mean finishing it next Sprint. It goes back to be ordered like anything else, and what the team learned while attempting it may leave the item looking less valuable than before.
Who owns it
Nobody, and that is what questions in this area are usually built on. Where the organisation has a Definition of Done, it is a standard all Scrum Teams must follow as a minimum. Where it does not, the Scrum Team must create one appropriate for the product. Notice who is absent from both sentences. The Product Owner does not decide it and neither does the Scrum Master, so an option naming either of them is describing an accountability the Guide does not create.
The Developers are named separately, and their obligation is to conform to the Definition of Done. Creating a standard and complying with one are different acts, which is why Developers quietly lowering the bar to finish a Sprint are not exercising self-management. It is the part of their work the Guide does not leave open.
Organisational standards and stricter local ones
Where the Definition of Done is an organisational standard, every Scrum Team follows it as a minimum. A team may apply stricter standards to its own work and may never apply looser ones, because the standard describes what the product requires rather than what the team would prefer.
The same logic settles the scaled case. Several Scrum Teams working on one product share one Definition of Done, since they produce one Increment between them, and parts built to different standards cannot be integrated into something usable.
What the Guide leaves open
There is no template. The Guide lists no criteria, sets no number of them and says nothing about when the standard may be revised, which is deliberate, because the quality a payments platform requires and the quality an internal reporting tool requires are not the same.
It is also not a Definition of Ready, an artifact Scrum does not have. A team running one has made a local agreement, which is reasonable so long as nobody mistakes it for a rule of the framework. Nor does the Guide ask anyone outside the Scrum Team to approve the standard, so a Definition of Done built around waiting for an external sign off usually describes an organisational impediment rather than a quality measure.