Count the experience (base and job) you win by minute or the total of experience you made during a session of experience.
Session : Enabled. You got 12000 base exp and 9000 job xp for 3 mins.
That means you did 4000 base exp / min and 3000 job exp per min.
@session : Give the status, total exp, xp per min in the current session
@session reset : Reset the counter
@session on : Turn on the counter for the current session
@session off : Turn off the counter for the current session
@session help : Give you details on the command in game
You can stop the session for a while and turn it on again without being reset.
The counter is being reset on reconnection.