Reflux is a term used to describe the backward flow or return flow of fluid in the body. There are several types of reflux including: esophageal reflux, gastroesophageal reflux, hepatojugular reflux , intrarenal reflux, and vesicoureteral reflux.

Reflux most often used in reference to GERD, or gastroesophageal reflux disease, a very common condition. GERD results from the relaxation of the muscles around the entrance to the stomach, which allows a back flow of food, stomach acid and digestive enzymes up into the esophagus. This is called acid reflux.

The term reflux can also refer to vesicoureteral reflux (VUR), a less common condition. In vesicoureteral reflux the flow of urine is abnormal.