The agile product backlog in Scrum is a prioritized features list, containing short descriptions of all functionality desired in the product. When applying Scrum, it's not necessary to start a project with a lengthy, upfront effort to document all requirements. Typically, a Scrum team and its product owner begin by writing down everything they can think of for agile backlog prioritization. This agile product backlog is almost always more than enough for a first sprint. The Scrum product backlog is then allowed to grow and change as more is learned about the product and its customers.
A typical Scrum backlog comprises the following different types of items:
- Technical work
- Knowledge acquisition
By far, the predominant way for a Scrum team to express features on the agile product backlog is in the form of user stories, which are short, simple descriptions of the desired functionality told from perspective of the user. An example would be, "As a shopper, I can review the items in my shopping cart before checking out so that I can see what I've already selected."
Because there's really no difference between a bug and a new feature -- each describes something different that a user wants -- bugs are also put on the Scrum product backlog.
The product owner shows up at the sprint planning meeting with the prioritized agile product backlog and describes the top items to the team. The team then determines which items they can complete during the coming sprint. The team then moves items from the product backlog to the sprint backlog. In doing so, they expand each Scrum product backlog item into one or more sprint backlog tasks so they can more effectively share work during the sprint.
Conceptually, the team starts at the top of the prioritized Scrum backlog and draws a line after the lowest of the high-priority items they feel they can complete. In practice, it's not unusual to see a team select, for example, the top five items and then two items from lower on the list that are associated with the initial five.
For more, check out this product backlog example.