Wi-Fi Protected Access (WPA)

WPA is a marketing standard put together by Wi-Fi Alliance.
WPA includes both authentication(802.1x) and encryption. It comes in:

• WPA Personal: pre-shared key authentication
• WPA Enterprise: TLS

WPA-PSK

WPA-PSK is a special mode of WPA providing strong encryption without access to a RADIUS server.

In this mode encryption keys are automatically changed (rekeyed) and authentication re-established between devices after a specified period referred to as the 'WPA Group Rekey Interval'.

WPA-PSK is far superior to WEP and provides stronger protection for the home/SOHO user for two reasons: first, the process used to generate the encryption key is very rigorous and second, the rekeying (or key changing) is done very quickly.