Product Backlog Refinement

As an activity, Product Backlog refinement has the following purposes in Scrum:

• Clarifying items on the Product Backlog that are too unclear to start work on. This is preferably done directly with the people you’re building the items for (the stakeholders)
• Breaking down items that are too big to pull into a Sprint (which generally also means that they’re too unclear)
• Re-ordering the Product Backlog as needed to make the upcoming Sprints as smooth and valuable as possible
• Adding or removing items from the Product Backlog as new insights emerge
• Estimating the effort involved in implementing particular items. This does not have to be as ‘formal’ as assigning story points (an optional practice in Scrum), T-shirt sizes or whatever sizing technique you use. A gut feeling (“Yeah, we know well enough what needs to be done and it feels doable in a Sprint”) is fine too