A sprints in Scrum, or otherwise known as an iteration, is the heartbeat of the Scrum cycle.
Sprints (or iterations) in Scrum are small and repeatable intervals of work in which developers complete the effort which was committed to. The outcome of a successful Sprint is usually a shippable product or version of of a product.
Durations of sprints can be 1 week (5 work days), 2 weeks (10 work days) or even 1 month (20 work days). A sprint could actually be of any per-decided length but they are rarely longer than 1 month.