The Sprint Backlog is the set of Product Backlog items selected for the Sprint, plus a plan for delivering the product increment and meeting the Sprint Goal.  It provides visibility of the team’s work during the Sprint.

Some characteristics are:

• Contains enough detail so that changes in progress can be understood in Daily Scrum
• Sprint Backlog belongs solely to the Development Team
• All Sprint Backlog Items are "owned" by the entire Development Team, even though each one may be done by an individual team member.
• The Sprint is over when its time-box has expired.

The Development Team is responsible to:

• Update estimates and remaining work as work is performed or completed
• Remove items if they are no longer needed to create a done piece of functionality
• Add work items as the team learns more about the work
• Total the remaining work at least for every Daily Scrum and project the likelihood of achieving the Sprint Goal; this should be done prior to the Daily Scrum

Note that Scrum does not concern itself with tracking time spent on the Sprint Backlog items.  The work remaining and date are the only variables of interest

The Development Team should not be interrupted during the Sprint. The work it selects for the Sprint should not be changed. The Sprint Goal should remain intact. However:

• As the selected Product Backlog Items are decomposed, the Sprint Backlog changes and may grow as the work emerges.
• The Product Owner can help clarify or optimize the Sprint when asked by the Development Team
• The Development Team may work with the Product Owner to remove or add work if it finds it has more or less capacity than it expected.