What's a session ?

Answer 1

A session could also end after a set period of time. For example a site might enforce the end of a session after a certain period of inactivity (like at a bank website). This way you have to reauthenticate in order to do anything else.

Answer 2

Here's a good tutorial about PHP session:

https://www.w3schools.com/PhP/php_sessions.asp

And a comprehensive definition related to session:

http://php.net/manual/en/book.session.php

Hth, cmiiw