A Sprint is different from an Iteration
In other frameworks under Agile, the term iteration is used to define the time period in which plan and develops an increment of functionality. So, why introduce a new term – sprint in Scrum.
The obvious answer [and correct one too] is that Scrum borrows a lot of terminology from Rugby [including the word Scrum]. A sprint in Rugby is a distance an athlete would travel from one end to another. Before an athelete or team would sprint, the team would quickly get together and plan how to go about it. During the sprint, an athlete would encounter opposition from the other team and might go ahead with the plan [if the plan still is good] or more likely alter the plan. You can anticipate but not predict the opposition. A sprint tests whether the team is a team, whether they are good or not and their ability to respond to change. It is clear to see why sprint is an appropriate terminology for Scrum. A sprint in Scrum is a time period (can be anything from 2 to 8 weeks) in which the team does whatever it can to develop software as per the features/ requirements that the Team has committed to. It is important to note that during a Sprint, the team not only iterates towards a final product solution, always improving on what they already have, but also take on some additional increments. Hence, product is developed iteratively and incrementally during a sprint. The term iteration can sometimes fail to capture the incremental part of product development during a sprint.