March 2018 broad core update
Google publicly confirmed a broad core algorithm update, establishing the naming convention used for every core update since.
What changed
Google confirmed on 12 March 2018 that a broad core algorithm update had rolled out during the previous week, affecting the appearance and ranking of some sites. It said there was no fix for pages that dropped, that the change was about better rewarding previously under-rewarded pages, and that publishers should keep focusing on strong content. Google did not give a precise start date, so the confirmation date is used here. This is generally treated as the first update of the modern core-update era.
Timing
Rollout began 12 March 2018. 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.