WEP/WEP2 and WPA/WPA2 are encryption technologies used in wifi connections. The only difference between WEP and WEP2 is the stronger 128bit key that the later uses. Likewise WPA2 offers all the features of WPA, adding stronger encryption, by implementing AES instead of TKIP. WPA in general uses additional tehniques and more efficient approaches to deal with WEP's issues. For more details have a look at the following articles, there's plenty more documentation if you make a search at the web.