A backlog is a prioritized list of tasks that teams need to work on within the scope of a project management strategy. It is derived from the requirements and roadmap of the project. Important tasks in the backlog are usually shown on top of the list to let the team know which tasks they need to deliver first. The backlog is often performed by iteration (scrum) or continually (kanban). Backlogs are very important because they serve to connect the development team and the owner.
The foundations of the backlog are the roadmap and requirements. It is the job of the product owner to prioritize the backlog based on the input from the designers, development team as well as the clients. Once the backlog has been built, there is a need for the development team to keep its pace attuned to the project. It is important to review the backlog before planning to ensure that the prioritization is accurate. Regular review of the backlog is termed as backlog grooming and is often used in project management. Along with the review, re-prioritization of work occurs which affect the estimates and may arise new requirements for the project.
This project management term is defined in the 5th edition of the PMBOK.