In Community, you'll notice that there are two separate sections called Members and Users.
Each of those sections serves a different purpose:
A Member holds all memberships, billing information, bookings, etc.
A User connects the Member to the members portal, e.g when you're enabling a member in order to grant them access to the members portal - more on that in this article - you're issuing permissions to their user that exists in the system. Under Community, the number next to Users displays how many members have credentials to the members portal.
You can see the different permissions that are being granted to Users depending on their Status in the system here.