Hello,
While try to move a topic on my forum appeared the message "Your Session has been expired." I tried it again with success but what means this message?

Hi,

Forumotion uses PHP engine to make the forums work. PHP is a server side programming language. Session is just a cookie that is stored in your browser that communicates with the server and let it knows who it is. You have already authenticated yourself while logging in. That request was then sent to the database so it could verify your account and then that first cookie that I told you about got registered in your browser.

For security purposes, these cookies aren't valid for ever. Each month, Forumotion cookies expires and you're forced to re-insert your login and password again. So, it was probably just your forum cookie expiring while you were doing something. Nothing to worry about it.

Ok, I understand it now but I was scared because I didn't saw this message again. The problem seems solved.

Thank you very much @Ace.