The product owner is responsible for defining and prioritizing the product backlog, which contains the features and requirements that the project team will deliver in each iteration. To ensure that the product backlog reflects the needs and expectations of the stakeholders, the product owner should validate the acceptance criteria with them before refining the backlog. Acceptance criteria are the conditions that a product feature or requirement must meet to be accepted by the stakeholders. By validating the acceptance criteria with the stakeholders, the product owner can ensure that they are clear, measurable, testable, and aligned with the project vision and goals. This will also help to avoid misunderstandings, conflicts, and rework during the iteration demos, as the stakeholders will have agreed on what constitutes a satisfactory product feature or requirement. References: PMBOK Guide, 6th edition, section 5.1.3.2; Agile Practice Guide, section 4.2.1