A retrospective format — popularized by Etsy's John Allspaw and the broader Site Reliability Engineering community — that examines a failure or near-miss with the explicit ground rule that no individual will be blamed. The goal is to maximize honesty about what actually happened so that systemic causes can be addressed.
Blameless does not mean accountability-free; it means accountability sits at the system level rather than the individual level. Done well, blameless retrospectives uncover the latent conditions that made a single human error catastrophic — and fix those conditions, not the human.