Gastroesophageal Reflux Disease, otherwise known as GERD, can be broken down quite logically. Gastro refers to the stomach, and esophageal refers to the esophagus. Reflux typically means to flow backwards opposite from the direction intended. Thusly, GERD is caused by the contents of the stomach making their way back up the esophageal tube, much like the explosions of an active volcano.