Definition:

intestinal rumbling caused by moving gas

Example:

"[The album] Earth 2 plunges you into the belly of a mastodon after a huge feast, and the sound is like the ensuing borborygmus." — Dave Segal, The Stranger, May 30, 2012

About the Word:

Borborygmus is onomatopoeic, or imitative – it sounds like the thing it describes. It's a New Latin word (Latin as used in scientific description and classification) that comes from the Greek borboryzein, "to rumble."