The "PS Button" is the large circular button with the PlayStation logo in the center of the DualShock 3 / Sixaxis controller. There is no "AOSS" button on the PS3 or its controller.
AOSS (AirStation One-Touch Secure System) is a Buffalo Technology feature for Wi-Fi router WPS-style push-button setup. It is not a PlayStation feature. Some routers have an AOSS button; the PS3 connects via standard WPS or manual Wi-Fi setup.
If your router has an AOSS button, you can use it during the "Wireless" setup by selecting "AOSS" instead of "Scan," but this is a router feature, not a PS3 button.