The Product Backlog Refinement session is not an official Scrum event, but it is a crucial activity that helps Scrum teams to achieve a shared understanding of the product backlog items in preparation for the sprint planning. Teams that adopt the product backlog refinement as a complimentary practice tend to have smoother sprint planning events. The number of refinement sessions within a sprint depends on various factors such as the state of the product backlog, the maturity of the product, the Scrum team’s availability and experience.