In the ScrumProcess, the larger of two InspectAndAdapt cycles are called Sprints. Sprints are 30-days* (WhyThirtyDays?) in length, and must result in a potentially shippable increment of software. (Of course, when using Scrum on non-software projects this rule would become "must result in something of actual value".)
* Current (2011) texts usually state either 2 or 4 week Sprints.