According to the Mayo Clinic, there is no difference between a belch and a burp. By performing this reflexive action, the body removes excess air that is in the stomach.
There are many ways for extra air to make its way into the stomach. Some people regularly swallow air during meals, especially if they consume food too quickly. Drinking carbonated beverages sometimes leads to too much air. Certain habits, such chewing gum, sucking on hard candies and smoking, also cause people to swallow air. Swallowing air itself is a nervous behavior for some individuals. Digestive conditions, including acid reflux and gastroesophageal reflux disease, make stomach acid back up into the esophagus. Sufferers repeatedly swallow to lessen the discomfort but wind up taking in too much air.