The number of times a query is searched per month, used to size opportunity for a target keyword. Reported numbers come from third-party tools (Ahrefs, Semrush, Moz, Keyword Planner) and are estimates derived from clickstream data, scraping, and Google's own monthly-rounded ranges. Volumes vary substantially between providers for the same query. "True" volume is only known to Google. For decision-making, the rule of thumb is to compare relative volumes between candidate keywords rather than treat absolute numbers as accurate.