A structured retrospective conducted after a project, launch, incident, or decision has concluded — particularly when the outcome was negative — to surface root causes and extract lessons that improve future performance. The medical metaphor is intentional: the goal is diagnostic, not prosecutorial.
The best postmortems are blameless (see Blameless Retrospective), examine systems rather than individuals, and produce a small number of specific, owned action items. Without those action items, a postmortem is a confession, not a learning event.