The letters of GERD stand for gastroesophageal (say: gas-troh-ih-sa-fuh-JEE-ul) reflux (say: REE-fluks) disease.
Gastroesophageal reflux is when the stomach's contents flow back up into the esophagus. The acid from the stomach irritates the esophagus and can cause problems like burning in the chest or coughing. When gastroesophageal reflux happens a lot and is severe, it's called GERD.