"hidd" stands for Human Interface Device Daemon. It is a core process in Mac OS X that lets you interact with the operating system using mouse, trackpad, keyboard and other human interface devices.
It has been known occasionally to create CPU overload problems. In this case you can restart your machine or kill it using a terminal window. While without "hidd" running you can't really use your machine, it normally restarts itself immediately so killing it should not be problematic.