A PLC is a Programmable Logic Controller. It is used quite a bit in industry for automation.... well it can pretty much be used for just about anything. When I was studying we had to control a washing machine with it as a project. Instead of designing a controller for a specific project you just get a PLC and programme it for what you want. The most common language is ladder programming (well when I was still studying it was). You used to have to do the programming on a PC and send it down the serial port to the PLC. The PLC consists of modules you add on. So you have one controller, which is the processor, and you just add on "output" modules for the number of processes you want to control. Siemens were very big into it. I think they still are.