WEP is "Wired Equivalent Privacy" click here
Its no longer sufficient as the encryption is flawed and can be broken in five to ten minutes. click here
What level of security does this give?
Well it would keep out most people and I guess its better than no encryption but it still not safe to use.
You are better off using WPA or WPA2 if your hardware will allow it.
Using WPA with at least 20 random characters would give you a very good secure network.