xPL stands for "eXtremely simPle protocoL". The xPL Project was started in January 2003. Its goal is to create a unified protocol to allow the control and monitoring of all devices within the home, whilst maintaining an unparalleled level of simplicity and ease of use.
SqueezeCenter natively provides an xPL plugin found under
Settings -> Plugins.
This means one can control the SqueezeCenter with home automation commands. The first step is to install xPL on a machine. The second step is to enable xPL support on your SqueezeCenter. Once there, you are ready to send xPL messages and control the SqueezeCenter via other resources than the SqueezeCenter web pages or the Command Line Interface.