GERD is a condition in which the stomach acid or contents from the stomach flow back into the food pipe (esophagus). The backwash (reflux) irritates the lining of the esophagus and causes GERD. Gastroesophageal refers to the stomach and the esophagus.
If regular brushing, flossing and popping innumerable breath mints does not work for bad breath, it is time to realise that the problem is deeper and beyond the mouth. GERD has a definite link to bad breath which is a rather embarrassing problem, causes for which sometimes can be medical.