Sixaxis (trademarked SIXAXIS) is a wireless gamepad produced by Sony for their PlayStation 3 video game console. It was introduced alongside the PlayStation 3 in 2006 and remained the console's official controller until 2008. The Sixaxis was succeeded by the DualShock 3, an updated version of the controller that, like the DualShock and DualShock 2 controllers, incorporates haptic technology – also known as force feedback. A Sixaxis controller can also be used with Sony's PSP Go via Bluetooth after registering the controller on a PlayStation 3 console.
The DualShock 3 was originally intended to be bundled with the PlayStation 3 in time for the console's launch. However, Sony was in the midst of appealing a decision from a 2004 lawsuit involving patent infringement claimed by Immersion. The two companies were at odds over the haptic feedback technology used in earlier PlayStation controllers. The legal battle led to a decision to remove the vibration capabilities from the PS3 controller's initial design, which became known as Sixaxis.
The term "sixaxis" is also used to refer to the motion-sensing technology in PlayStation 3 controllers. It is a contraction of "six axis", which refers to the ability to sense motion in all axes of the six degrees of freedom. The term is also a palindrome.
Source: Wikipedia, "Sixaxis," available under the CC-BY-SA License.