The term “Session” is used many times in the GAS documentation but nowhere does the documentation explicitly state what a session is. It is referred to in many places such as definition of uaproxy, configuration elements SESSION_COOKIE, SESSION_DIRECTORY, and how to get a Session Id .
The best way to understand is to look at the Architecture diagram, when a Genero Web application is started, a VMProxy (uaproxy) and DVM (fglrun) is started. Any Genero applications launched via RUN from that initial program are considered to be part of the same Session. They will be managed by the same proxy process and have a unique identifier, the Session Id.
Read more at
https://4js.com/ask-reuben/ig-240/