When the ProductOwner is ready for a feature to be developed, it is moved from the ProductBacklog to a SprintBacklog. So at first its estimate may be large and unwieldy. 

So, at the beginning of the ScrumSprint, during SprintPlanning, such a feature might be split into multiple, smaller items for implementation. In this way, the feature description and estimate are better defined, and sometimes new tasks/features are discovered.

Likewise, during a Sprint, if entirely new tasks are discovered, they can be added to the SprintBacklog. It is also possible, however, that a new task ''not'' related to the SprintGoal is tossed back into the ProductBacklog, to be prioritised by the ProductOwner according to business priorities.

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CategoryScrum