According to the PMBOK Guide, a retrospective is a meeting held by a project team at the end of a project or process (often after an iteration) to discuss what was successful about the project or time period covered by that retrospective, what could be improved, and how to incorporate the successes and improvements into future iterations or projects. In an agile project, retrospectives are usually held at the end of each iteration or sprint, regardless of the size or duration of the increment, milestone, or progress. The purpose of retrospectives is to enable continuous improvement and learning throughout the project life cycle, not just at the end of a major phase or deliverable. Therefore, the project manager should organize the first team retrospective when the work is progressing well through the team, which implies that the team has completed at least one iteration or sprint and has some feedback to share and act upon. References: (Professional in Business Analysis Reference Materials source and documents)
* PMBOK Guide, 6th edition, Chapter 4, Section 4.6.1.2, page 123
* PMBOK Guide, 6th edition, Appendix X3, Section X3.2.2, page 718
* PMI PMP-Project Management Professional Practice Exam Q. 781 to 790