Hello Michael
I understand your confusion, and I believe it is an issue with terminology. WEP is actually defined as a security algorithm that is used in the IEEE 802.11 standard wireless networks. This algorithm has several configuration parameters, one of which is the type of supported authentication. This simply refers to how the WEP algorithm is applied to a wireless communication.
The first, which is Open authentication, doesn’t require credentials, so anyone can connect to an Open Authentication WEP access point, so any client within range can freely connect. However, the actual data being transmitted is encrypted.
The second, shared key authentication, does require credentials, and so not “just anybody” can connect to the access point. The actual data being transmitted is still encrypted.
As for the shared and pre-shared key, the difference is as follows:
WEP uses a shared key, which means that every client uses the same key. It is shared among multiple users. A pre-shared key is simply a key that has been shared before the time of the actual authentication. This is the general definition of these terms. Of course, this does not prevent you from “pre sharing” a shared key, but in the framework of WEP (shared) and WPA2 (pre-shared), this is the meaning.
I hope this has been helpful!
Laz