Commonly referred to as GERD or acid reflux, gastroesophageal reflux disease is an uncomfortable condition where the liquid that is in a person's stomach backs up or refluxes into the esophagus. Causing inflammation and damage to the esophagus lining in some patients, this can range from mild and uncomfortable to a very serious problem. Since this liquid is filled with both pepsin and acid and even bile, the reflux can cause pain and burning sensations.