The Definition of Done is a formal description of the state of the Increment when it meets the quality standards required for the product. The purpose of the Definition of Done is to:
During the Sprint, it helps the Developers identify the work remaining for an Increment to be ready for release by the end of a Sprint (B), by providing a clear and shared understanding of what "Done" means for each Product Backlog item and the Increment as a whole. It creates transparency into the state of the Increment when it is inspected at the Sprint Review, by ensuring that everyone involved in the product development has the same expectations and criteria for evaluating the value, usability, and quality of the Increment. It guides the Developers when creating a forecast at the Sprint Planning (D), by enabling them to estimate how much work they can realistically complete within a Sprint, based on their capacity, skills, and Definition of Done.

Explanation
Explanation:
Product Backlog items should be clear enough and have enough information for the Product Owner and Development to understand the work that needs to be done and to create a forecast of Product Backlog items to implement the Sprint Goal. Nothing stops the flow of Sprints, for example, we do not delay the Sprint because the items are not ready. In such cases, the "unready" items would be selected for the Sprint anyway and refined during the Sprint.
In the case that the Product Backlog items are not clear enough, the Development Team forecasts the most likely Product Backlog items to meet the goal and create a Sprint Backlog based on a likely initial design and plan. Once the time-box for the Sprint Planning meeting is over, start the Sprint and continue to analyze, decompose, and create additional functionality during the Sprint. At the end of the Sprint, the Scrum Team can discuss in the upcoming Sprint Retrospective why this happened and what changes will make it less likely to recur.

At the end of a Sprint, the new Increment must be `Done', which means it must be in useable condition and meet the Scrum Team's definition of `Done'. Scrum Team members must have a shared understanding of what it means for work to be complete, to ensure transparency. This is the Definition of Done for the Scrum Team and it is used to assess when work is complete on the product Increment.

People personally commit to achieving the goals of the Scrum Team by doing their best and helping others.

Explanation/Reference:
Explanation:
A Product Owner or Scrum Master can be dedicated to one team OR participate as a member on more than one team. How much time they spend with each team will directly impact effectiveness of the team.