It's a WiFi to Ethernet bridge. There are many out there so I'll link one and stop there.
https://www.amazon.com/IOGEAR-Universal-Ethernet-Adapter-GWU627/

OK, there are such devices but that hidden SSID doesn't play well with a lot of devices. We saw a lot of complaints so I won't debate why it's like that. It's not as if adds to security.