To step just a little bit more into the technical side of things: A session in Mendix is a domain model entity in the system module, which is used for storing the ‘session-specific’ information from an user, such as when he/she has been active for the last time. You might perceive the session a bit like the timeframe in which the user is using your application. The session is retained untill it is cleaned up by the application after the user logs out.

From a developers perspective; Sessions are also available by defauly in microflows as the $CurrentSession object. As such, it can be used for client-based or ‘session-specific’ actions. By creating associations between the session entity and other (non-)persistant entities, the other entities can also become available by retrieving them from the CurrentSession object.

A session in mendix is when any user or anyone with a user role goes on the system

the system will increment the sessions depending on the number of the logged users 

for example you have a simple login user main page admin main page registration system and you ran the application before the sign in feature is triggered  the application will reserve a session for the anonymous user (if you have that enabled ) and after signing in it will reserve another session for the logged user and all of that can be traced in the mendix console if you’re running locally or on the mendix website when running on the cloud 

if i am wrong about any of this i would be happy to be corrected 

Regards Ahmad Jaber