|Concise description of knowledge that results from an after-the-fact analysis of a project, a new technique, or the application of new knowledge and that can be communicated through mechanisms such as storytelling, debriefing and summarized databases. It is the opposite of good practices. Lessons Learned are reports of unsuccessfull experiences that must be widely spread troughtout an organization to preclude recurrence of unsuccessful outcomes, preventing mistakes to be made again, and to promote recurrence of successful events. 
Is a generalization derived from evaluation experiences with programmes, projects or policies that is applicable to a generic situation rather than to a specific circumstance and has the potential to improve future actions. A lesson learned summarizes knowledge at a point in time, while learning is an on-going process.