Velocity is a measure of the speed at which an agile software development team completes work items. This measurement is calculated by counting the units of work completed within a defined interval, such as a sprint.
What defines a unit of work is chosen by the agile team. This could be real measurements, like the number of hours worked or the number of items completed, or more abstract measurements, like story points or effort estimates.
By knowing velocity, teams can estimate how much work they can complete in the future based upon how quickly they completed work in the past.