Agile Overview → Planning → Sprints
A sprint is where all of the actual work happens. Every day, team members gather in daily standup and quickly state what they have done, what they are going to do, and whether they have any impediments. Sprints rely on a team's velocity to determine how much work can be done in a future sprint and on a team's burndown chart to gauge how well a team is completing its work in a current sprint.
The primary goal of a sprint is to add a new piece of shipping software to an application. This could be one or more new features, a small collection of improvements (fixed defects), and so on, as long as the completed (and accepted) work results in something of actual value for a customer.