The SSID is the network’s “name” — for example “Office” or “Guest”. One access point can broadcast several SSIDs, each belonging to a different network (VLAN) with its own password and rules.
Businesses often run separate SSIDs for staff, guests and, where needed, IoT devices.
Example
A café has two SSIDs: “Cafe-Staff” for the checkout and “Cafe-Guest” for customers.