It's mildly technical.
I understand not everyone wants to learn all about wifi and routers but let me address the "working for 4 years" issue.
Here's the deal. Today we have a lot more wifi users. We also have new "kiddie scripts" that hijack, interfere and SMACK DOWN other people's connections. This is why what worked for years can stop working. This is why the forum sticky came to be so that we don't go a dozen posts and repeat the same advice for every member.
Back to "What is SSID?" For that you hit the web, your router manual and more. This forum is unpaid volunteers and other members. Beyond the sticky posts there are few tutorials given in replies.
It's more like the people that stop to help you change a tire or push you out of a ditch. You get to pitch in.