Borborygmus is a rumbling sound made by the body, which is caused by gas moving through the intestines. Using layman's terms, it is the sound of a stomach growling, gurgling, or rumbling.
The sound you're hearing during borborygmus is the sound of your body going through the normal digestive process.
This contraction and movement occurs on a fairly regular basis, but we tend to hear it most of all when we are hungry, simply because the movement is taking place in an “empty” area. Not only does this make it more audible, but it means that the stomach has less food and more gas to move, which can result in bubbling and shifting that will lead to audible sounds.
Borborygmus can also occur when food doesn't digest properly, since that sometimes leads to excess gas in the system, and again it can be felt moving and be heard rumbling as the stomach muscles contract to move it onward.
See borborygmus in Webster's New World College Dictionary
noun pl. borborygmi
Origin: ModL < Gr borborygmos < borboryzein, to rumble
See borborygmus in American Heritage Dictionary 4
noun pl. bor·bo·ryg·mi (-mīˌ)
Origin: New Latin
Origin: , from Greek borborugmos
Origin: , of imitative origin.
Learn more about borborygmus