Blogger's about page sports white text on a white background. I made it through account creation, but more than that would drain my will to live below critical levels. It's lame that they can't make simple things work without resorting to Javascript. I still want one though. Just so no one is left out, I'll explain what they are.
File descriptors are like channel numbers.
When a program wants to read or write a file, it assigns a number to the file, and all the read and write commands use that number to refer to the open file. One of the great things that makes unix worth using is that you can plug programs into each other pretty easily. So instead of one program printing its output to the screen and the next program reading from the keyboard, you just plug them together so that the first one feeds its output into the second one. These are called pipes. Decent command shells will let you arbitrarily plug anything into stdin and send stdout and stderr independently wherever you want, to files, other windows, or into other programs.