A Sprint burndown chart is a visual measurement tool that shows the completed work per day against the projected rate of completion for the current project iteration. It is a tool for the Scrum Team to visualize how quickly they are working through the customer's user stories, reflecting how much work is left to be done. The horizontal axis represents time, and the vertical axis represents cards (stories). All members have real-time access to what remains in the Sprint Backlog in terms of work.

'Done' is a shared understanding by the Scrum Team about what it means for work to be complete. This varies significantly per Scrum Team, but can consist of criteria regarding quality, functionality, design, and more. The purpose of a clear definition of 'done' is to articulate what expected work should be delivered at the end of a Sprint. The Scrum Team makes transparent what 'done' means in its specific context. It allows teams to assess when work is complete on a product backlog item or an entire sprint.

Estimation and velocity is a concept that involves quantifying the amount of work a team can handle in a sprint. Estimation is usually done in story points, which provide a relative measure of effort required to complete features of a product. Velocity, on the other hand, is how much work a team can accomplish in a normal sprint. This measure helps the team to predict how many sprints will be needed to complete the project or to reach a certain milestone.