1. Also known as belching, ructus, or eructation, it refers to the release of gas from the digestive tract (mainly esophagus and stomach) through the mouth.
2. To allow air from the stomach to come out through the mouth in a noisy way.
3. To gently rub a baby's back to help air to come out of his or her stomach.

It is often accompanied with a typical sound and sometimes an odor.

4. Etymology: an informal version of belch. Apparently an American-English imitation of the sound of belching.