The percentage of sessions in which a user landed on a page and left without further interaction. In Universal Analytics (retired July 2023) "no further interaction" meant a single pageview. Google Analytics 4 redefined the metric in 2023 as the inverse of "engaged sessions" — a session is engaged if it lasts 10+ seconds, fires a conversion, or has 2+ pageviews — meaning GA4 bounce rate is not directly comparable to UA bounce rate. Bounce rate has never been a confirmed Google ranking signal; treat it as a UX diagnostic, not an SEO KPI.