In regards to memory usage, what are buffers?

Question

Just took a look at the memory usage (with free -m) on one of my Ubuntu servers and saw this:

             total       used       free     shared    buffers     cached
Mem:           751        624        127          0        256        236
-/+ buffers/cache:        131        619
Swap:          299          0        299

1. What is a buffer?
2. If something needed RAM to process something, would a buffer give up its allotment (like cache would)?
3. Is there any way I can find what's using the 256MB of memory for buffer?
4. Should I be worried?

Answer 1

1. The developers of the linux memory management have a short technical description of it (look for the "Buffer Cache" topic).
2. Buffers that aren't needed at the moment can make way for more urgent memory needs.
3. The kernel is using it.
4. No.