What does Velocity measure in Agile?

Velocity in Agile is primarily a measure of the amount of work completed by a team within a specific iteration or sprint. Specifically, it indicates the number of story points or units of work a team can complete over a given time frame, which typically aligns with a sprint duration.

The correct choice highlights that velocity represents the rate of work acceptance over time, as it not only considers the completed tasks but also the context of team performance across iterations. This measure helps teams estimate their capacity for future sprints based on past performance, facilitating better planning and management of workload.

Considering the other options: measuring the speed of task completion and the number of User Stories developed does not provide a holistic view of a team's delivery capacity since these metrics can vary significantly without reflecting actual effort or efficiency. Total effort estimated for tasks relates more to initial planning than to actual outputs, which is not the focus of velocity as a performance measure in Agile.