[A] Refinement is a part-time activity during a Sprint between the Product Owner and the Development Team.

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Product Backlog Refinement is the act of adding detail, estimates, and order to items in the Product Backlog. This is an ongoing process in which the Product Owner and the Development Team collaborate on the details of the Product Backlog items.

Refinement usually consumes no more than 10% of the capacity of the Development Team. During Product Backlog Refinement, items are reviewed and revised, based on feedback from the Development Team and possibly other stakeholders or experts.

However, items can be updated at any time by the Product Owner or at the Product owner’s discretion