Fred
Unconfirmed March 2017 quality update associated with heavy losses at ad-dense, thin affiliate and low-value content sites.
What changed
In early March 2017 tracking tools recorded a sharp volatility spike concentrated on sites with thin content and aggressive monetisation through display advertising and affiliate links. Google acknowledged that updates had happened but declined to confirm a distinct system, and a Google engineer's joking suggestion that all unnamed updates be called "Fred" became the industry name. Only month-level precision is documented, so the date here is the first of the month.
Timing
Rollout began 1 March 2017. No completion date was announced. Rankings typically remain unstable for the whole rollout window, so measurements taken inside it are not a reliable read on the outcome.