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Story is a feature that can be tested separately, and is part of an Epic.
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Defect is a direct failure or fault that is a direct consequence of the acceptance criteria found during User Acceptance Test on a Story. A
Sub-task is an activity that needs to be performed to complete a higher-level issue type. It's always part of another issue type.
At the same level as Story, other Product Backlog Items exist with slightly different meanings:
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