What is a hidden network

A hidden network is a wifi network that is available, but the name isn't broadcasted. When you search for wifi networks, it doesn't come up in the list. Your device can detect it, it just doesn't know anything about it so you would need to know the network name (SSID), type of security, user name & password in order to join.

I found this article that explains it.

Join a hidden Wi-Fi network on Mac - Apple Support

I hope that helps you ☺

A hidden network is generally defined as one that is not broadcasting its SSID. If you are seeing that name displayed in your wi-fi list, it is very possible that the wi-fi administrator has jokingly named their network that name.