Max Value ' Guest users'

I' ve been comparing one of my firewalls against the Fortigate Maximum Values Table to make sure everything is good. (Looking at a 300c for the record). In the user and device section, there is a line that says ' Guest Users' (limited to 500 on the 300c). Most of the other lines are self explanatory, number of FSSO servers, local users, etc, but this one isn' t quite clear. Does anyone know what the Guest Users maximum limit means?