Gastroesophageal reflux disease (GERD) is a more serious form of gastroesophageal reflux (GER), which is common. GER occurs when the lower esophageal sphincter (LES) opens spontaneously, for varying periods of time, or does not close properly and stomach contents rise up into the esophagus. GER is also called acid reflux or acid regurgitation because digestive juices—called acids—rise up with the food.
The esophagus is the tube that carries food from the mouth to the stomach. The LES is a ring of muscle at the bottom of the esophagus that acts like a valve between the esophagus and stomach.