What is Sprint Backlog in Scrum?
The sprint backlog is the subset of items from the product backlog intended for developers to address in the upcoming sprint. Developers will fill this backlog until they feel they have enough work to fill the sprint, using past performance to assess capacity for the next sprint, using this as a guideline of how much 'effort' they can complete.
Work on the sprint backlog is never assigned (or pushed) to developers; team members pull work as needed according to the backlog priority and their skills and capacity. This promotes the self-organization of the developers.
The sprint backlog is a developers' property, and the developers provide all included estimates. Although not part of Scrum, some teams use an accompanying board to visualize the state of work in the current sprint: ToDo, Doing, Done.