“Average All Total Users by Month” is referring to the cumulative total number of user accounts / signups. The “by Month” part is a little misleading in this context, it’s just showing how the total number of users has changed, with a data point for each month.

“Monthly Active Users” aka MAU is a different metric and, in my opinion, is more relevant metric for looking at social media usage. Monthly active users gives a more accurate view of how much a social media platform is being used. According to fediverse.observer, the number of monthly active users, listed as “Average All Active Users by Month”, is around 1.73 million.

There are different sources that give different numbers in that similar range, so for the graphic I just put approximately 1.5 million for simplicity.