A thin client is a PC which runs a stripped down version of Windows (usually running one program). It doesn't have a harddrive, CD drive or other moving components. The device has less heat (meaning no fan or a notebook style one) and is usually designed to run 24/7. Leave it in a closet with a copy of Windows Remote Desktop or Real VNC running on it as well so that you can access it through your home network, but by and large just ignore it.