more /var/log/messages and read it a bit. They're labeled.
Serial console is a console running off a serial port on a server. You connect to it with a terminal program over a serial line. This allows, for example, a rack mounted server without a monitor or keyboard to be easily managed. Console servers are devices set up to allow you to connect multiple serial consoles on multiple servers to one device. You ssh to the console server and choose the server you want to talk to. Many vendors have such devices off the shelf, or you can build your own. I built my own: http://blogs.umass.edu/choogend/2008/05/23/ammonoidea/
using an old iMac with Mac OS X. You could do the same with an inexpensive linux box. People often have a laptop that they carry into a server room to access servers by serial console. Switches and routers also often have a serial console and can be accessed in the same way. It gets you to the management interface.