What is SSID?
SSID is the public name of a wireless network, for example the SSID of a new Linksys router is “Linksys” unless the user changes it to something else. When you browse the available wireless connections close enough for you to detect and connect to, you are looking at each routers SSID.
It’s a ‘beacon’ sent out at regular intervals by typically-configured wireless access points and routers - it is used to make it easier for anybody nearby to discover the existence of the wireless network and connect to it. Often it’s set by the wireless manufacturer to something like “LINKSYS” or “Netgear” or the like, which is a tipoff to hackers who may want to engage in some mischief with your network and PCs. The typical wireless unit has an administrative user interface that you can use to change the SSID to something nonstandard (as the OP has done) or to turn it off.
SSID is your wireless network’s “name”. The wireless router will broadcast it at intervals so any PC within range can “see” it and try to connect, which is where the security and encryption comes in. I turn it off, which is OK as my PCs know to look for it but if I have a new PC (well, new wireless card) I have to turn it on until the new one is house trained !
Determined hackers can still breach but like deadbolts etc, most will just go in search of easier prey.