Product Backlog
An emergent, ordered list of everything known to be needed in the product, owned and ordered by the Product Owner.
What it means
The Product Backlog is the single source of work for the Scrum Team. It is never complete; it evolves as the product and its environment evolve, capturing requirements, fixes, and improvements as backlog items.
Each item can carry a description, order, estimate, and value. Higher-ordered items are usually clearer and more detailed than lower-ordered ones, a practice sometimes called progressive refinement.
Common mistakes
The Product Goal lives as a commitment attached to the Product Backlog, giving it a long-term objective beyond any single Sprint. Refinement is the ongoing activity of adding detail, estimates, and order to backlog items.
Example
A Product Owner keeps 40 items in the Product Backlog, with the top eight refined and ready for the next Sprint Planning session.