Gastroesophageal refers to the stomach and esophagus. Reflux means to flow back or return. Therefore, gastroesophageal reflux is the return of the stomach’s contents back up into the esophagus. In normal digestion, the lower esophageal sphincter (LES) opens to allow food to pass into the stomach and closes to prevent food and acidic stomach juices from flowing back into the esophagus. Gastroesophageal reflux occurs when the LES is weak or relaxes inappropriately, allowing the stomach’s contents to flow up into the esophagus. The severity of GERD depends on LES dysfunction as well as the type and amount of fluid brought up from the stomach and the neutralizing effect of saliva.