Definition: A sprint retrospective is a meeting at the end of a sprint where the team reflects on how the sprint went. It typically asks three questions: what went well, what did not go well, and what can be done to improve.
So what? Retrospectives are where teams turn experience into change. For testers, they're a chance to raise problems such as performance testing being squeezed, and agree how to fix them next sprint.
Examples: A team noting that performance regression runs kept slipping and agreeing to schedule them overnight. Running a retrospective while product owners carry out user acceptance testing.