The network key is the sequence of numbers that defines the network from others' networks.
Here is some info on how to find your network key if you do not know it. Hope this helps!
The network key is a code or password one must enter into a computer. This pass code is sent to the router, and in turn the router connects to the Internet.
A wireless network key is used to secure a wireless network with a specified password. These passwords are required to gain access to the Internet connection and files on the network. Network keys are commonly encrypted with Wired Equivalent Privacy (WEP) or Wi-Fi Protected Access (WPA) types of security. The higher the bit size of a password the more letters, numbers or characters are involved in the password