Google Core Update

A core update is a revision of how Google assesses relevance and quality across the web, not a fix for one signal and not a penalty. Google confirms core updates publicly, and each rollout takes days or weeks. A site that drops has not necessarily done anything wrong: other pages may now be judged more useful for the same searches. Spam updates, which deal with sites that break Google’s spam policies, are a separate thing.

Google’s advice after an update is to avoid quick fixes, wait at least a week after the rollout finishes before analyzing Search Console data, and compare that period with the week before the update began (Google Search Central).

Then look honestly at the pages that lost ground. Ask whether each one is the most helpful, accurate and complete answer for the people searching, and improve it for them rather than for the algorithm. Changes like that are the ones Google says hold up over time.