How are "active members" defined in the lodestone?

[JWag12787]

In the lodestone's info for each FC there's a count for "active members." Does anyone know how this is defined? Is it the number of players that have signed on in the past x days?

I didn't see any other place to ask this.

Active is a bad use of the term on the Lodestone.
I believe it's just their total enrollment. It seems to match my FCs count, even though a good many have been idle for almost a year now.