When a wireless network broadcasts it includes the network name, called a Service Set Identifier (SSID). Most commonly the SSID will be a user-friendly name to help people identify which network they want to connect to (e.g. Smith WiFi, Friendly's Guest, etc.). Disabling SSID broadcast will still allow the network to be visible to nearby devices but in order to connect to the network they will need to know the SSID (as well as a password/key if configured).
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, …