A Wireless Access Point's SSID Broadcast is what allows a person or computer to easily identify a wireless network, turning this off will help mask/hide a network's identification.
In IEEE 802.11 wireless local area networking standards, a service set is a group of wireless network devices that are operating with the same networking parameters.
Service sets are arranged hierarchically,: basic service sets (BSS) are units of devices operating with the same medium access characteristics (i.e. radio frequency, modulation scheme etc.), while extended service sets (ESS) are logical units of one or more basic service sets on the same logical network segment (i.e. IP subnet, …