Gastroesophageal reflux disease is a condition in which stomach acid repeatedly flows back up into the tube connecting the mouth and stomach, called the esophagus. It’s often called GERD for short. This backwash is known as acid reflux, and it can irritate the lining of the esophagus.

Reference: https://www.mayoclinic.org/diseases-conditions/gerd/symptoms-causes/syc-20361940