Hidden networks are types of Wi-Fi which have their SSID broadcast disabled. This means that the Wi-Fi name of the router will not show on the list of available networks whenever a wireless device or computer searches for networks within range.
This article will show you how to connect to the Wi-Fi with a hidden SSID. Before proceeding, make sure that you know the following:
2. Wireless security type
3. Wi-Fi password or passphrase
Step 1:
Click on the AirPort® icon located at the upper right corner of your desktop screen then select the Join Other Network… option.
Click on the AirPort® icon located at the upper right corner of your desktop screen then select the Join Other Network… option.
Step 2:
Enter your wireless Network Name (SSID) and select your wireless Security type.
Step 3:
Enter your wireless Security key or Password, then click Join.
Enter your wireless Security key or Password, then click Join.
QUICK TIP: You may tick the Show password box to view the wireless security key or password that you entered. You may also tick the Remember this network box if you want the computer to automatically connect to the network when it is in range.
Your computer should now be connected to the Wi-Fi. The SSID will then be displayed when you click on the AirPort 
icon.
icon.