The "Definition of Done" (DoD) is a checklist that specifies the criteria that must be met for a user story or product increment to be considered complete by the team. It provides a shared understanding among team members and stakeholders of what it means for work to be finished. The DoD ensures that all user stories meet a minimum quality standard and are ready for production or release. It is not related to when the team is done with the iteration (B) or with estimating user stories (C).