It's weekly active users, There is literally no other context that needs to be presented. The worst you can assume without outright fraud is the number of users

It's weekly active users, There is literally no other context that needs to be presented. The worst you can assume without outright fraud is the number of users who send at least one query every week. Open AI don't need to report any numbers to see it's incredibly widely used. The site has had over 1.5B visits every month since March 2023.