SSID is an acronym for Service Set IDentifier. More commonly it’s the “network name” that’s assigned to a Wi-Fi wireless access point.
The SSID is typically broadcast by a Wi-Fi access point to announce its presence, and allow computer users to identify the access point and network that they might then connect to. Broadcasting the SSID is actually optional, and can be used to keep a network from appearing in “nearby networks” types of lists.