People tend to use the terms Sprint, Iteration, and Time box interchangeably. For the most part this is true, but there is some nuance:
Sprint is a term popularized by Mike Beedle and Ken Schwaber in creating the Scrum methodology. They chose the word because it implied a desire for fast pace. It’s not a death march (Yourdon), its a sprint.
Iteration has no inherent meaning except for repetition. It is used to describe the cyclic exercise of a common set of practices. In that light, even a quarterly release strategy with a waterfall or phase gated delivery in each release can be described as iterative. Sprint is a form of iteration within the Scrum methodology, and it is recommended to be no longer than 4 weeks in length.
Time box describes a measurement and planning strategy where we are going to plan based on a fixed amount of time and a variable amount of work rather than a traditional project which is the opposite. Time boxing as a iterative practice means that each iteration is a fixed length, and we plan what we believe can be completed inside the box. If consistent size boxes are used (e.g. always 2 weeks) then we can build a consistent reporting and measurement cadence, and a consistent planning cadence as well. Sprints are in fact, time boxes and Scrum practices a regular reporting, measurement and planning practice around the Sprint as a means of increasing information flow.
Within the agile practice community, there is a notion that exercising all of the skills or practicing all of the activities performed by the cross-functional team in the same iteration or sprint is valuable, for two reasons:
2) The practices around an activity should not be adjusted unless there is unless there is information about that activity.
In each sprint all of the “phases” of software development are executed, so that the risk and effort involved in those activities can be understood by the team, and adjustments to the plan and/or team practices can be made based on the information that comes from performing the activities.
Each sprint has a reflective meeting called a retrospective, where we evaluate the information that flowed from the exercise of practices, and decide whether to adjust the way the team does things.
So – the Sprint (or any other agile iteration framework) serves the following purposes:
1) Pacing – It emphasizes the pace and urgency of the delivery team.
2) Planning – It provides a container that is used to plan and measure delivery
3) Practice – It provides an iteration framework for ensuring that all activities
needed by the delivery process are performed frequently.
4) Information – It provides a consistent and frequent source of information about the
progress of and obstacles to all activities needed for delivery.
5) Adaptation – It provides a framework for tuning and adjusting each of the activities
needed for delivery.
6) Improvement – It provides an opportunity to reflect and improve each of the activities
needed for delivery.