Lessons learned is a two word phrase that refers specifically to the project management related input and output device that represents the knowledge, information, or instructional knowings that have been garnered through the process of actually completing the ultimate performance of the respective project. The concept of the lessons learned can also be referred to as the project record. Lessons learned for the most part are customarily included as part of the overall lessons learned knowledge base. As part of the utilization of the lessons learned knowledge base, the project team takes care to compile a thorough and useful historical stockpile of relevant information as to these lessons learned. These lessons learned, once part of the database, provide background and information about the previously made project selection decisions as well as in regards to any and all previous pproject performance. The lessons learned knowledge base can be updated throughout the project.
This term is defined in the 3rd and the 4th edition of the PMBOK.