The Secret Key
As was previously mentioned, WEP incorporates two main types of protection: a secret key and encryption. The secret key is a simple 5- or 13-character password that is shared between the access point and all wireless network users. This key is all-important to WEP in that it is also used in the encryption process to uniquely scramble each packet of information with a unique password. This ensures that if a hacker cracks one packets key, he won't be able to view every packet's information.
To do this, WEP defines a method to create a unique secret key for each packet using the 5- or 13-characters of the pre-shared key and three more psuedo-randomly selected characters picked by the wireless hardware.
For example, let's assume that our pre-shared key was "games". This word would then be merged with "abc" to create a secret key of "abcgames", which would be used to encrypt the packet. The next packet would still use "games", but concatenate it this time with "xyz" to create a new secret key of "xyzgames". This process would randomly continue during the transmission of data. This changing part of the secret key is called the Initialization Vector because it initializes the encryption process for each packet of data sent.