What does it mean by buffer?
Imagine that you're eating candy out of a bowl. You take one piece regularly. To prevent the bowl from running out, someone might refill the bowl before it gets empty, so that when you want to take another piece, there's candy in the bowl.
The bowl acts as a buffer between you and the candy bag.
If you're watching a movie online, the web service will continually download the next 5 minutes or so into a buffer, that way your computer doesn't have to download the movie as you're watching it (which would cause hanging).
The term "buffer" is a very generic term, and is not specific to IT or CS. It's a place to store something temporarily, in order to mitigate differences between input speed and output speed. While the producer is being faster than the consumer, the producer can continue to store output in the buffer. When the consumer gets around to it, it can read from the buffer. The buffer is there in the middle to bridge the gap.
If you average out the definitions at http://en.wiktionary.org/wiki/buffer, I think you'll get the idea.
For proof that we really did "have to walk 10 miles thought the snow every day to go to school", see TOPS-10 Monitor Calls Manual Volume 1, section 11.9, "Using Buffered I/O", at bookmark 11-24. Don't read if you're subject to nightmares.