A person who posted/commented in the last 30 days

From the docs: "Lemmy also shows counts of active users for your site, and its communities. These are counted within the last day, week, month, and half year, and are cached on starting up lemmy, and every hour.

An active user is someone who has posted or commented on our instance or community within the last given time frame. For site counts, only local users are counted. For community counts, federated users are included."

https://join-lemmy.org/docs/contributors/07-ranking-algo.html

Very useful. Finally something written in a way that everyone can understand

Well notbexactly. Just a faster way to stop spam. Block must be motivated of course, and each instance decides per se