Accumulation of gases in the stomach or bowels as a result of indigestion or swallowing air when eating, especially when eating rapidly. It is also caused by the fermentation of certain foods, particularly beans, carbonated beverages, vegetables, fruits, and grains. Air in the stomach may be expelled from time to time through the mouth as a belch, whereas that in the bowels may be expelled through the anus.
This advertisement came in a catalogue, including picture of the cushion on an aircraft seat with "carbon layer traps odours" printed on top: The Flatulence Filter (TM) is a breath of fresh air for you and your fellow passengers! Flying can cause many travellers to experience uncomfortable intestinal gas, which in turn can lead to embarassing wind. And at 30,000 feet, it's difficult to blame the dog! The Flatulence Filter looks like and ordinary seat cushion but contains an activated carbon air filter that absorbs odours immediately and lasts up to 12 months. Ideal for aircraft, train or car travel, it has a handy carrying handle.
In certain cultures belching after a meal may be considered a polite indication of satisfaction with the meal.