Velocity
A measure of the quantity of work a team can tackle during a single sprint. It is calculated by adding the story points of all fully completed user stories.
Impact
Velocity is for capacity planning, not for performance management.
Weinto take
Velocity is not Value. A team can have high velocity (shipping lots of junk) and zero value. We measure Lead Time to Value (how long from idea to customer hand) rather than just pure velocity.