You can specify that a particular network your device connects to is “private” or “public”. The key difference is whether other devices on the same network are allowed to see, and maybe connect to, your device.
Your home network might be an example of a private network – in theory the only devices on that network are your devices, and devices owned by your family. So you might be fine with those other devices being able to see yours. We call that “discoverable” because all the devices on that network are allowed to “discover” each other.
The Wi-Fi at your local coffee shop, however, is a public network. Most of the other devices connected to it belong to strangers and you’d probably prefer they not be able to see, connect to, or “discover” your device.