Reflux is a term meaning "to flow backwards" or "to return".

In chemistry, reflux is a distillation technique involving the condensation of vapors and the return of this condensate to the system from which it originated.

Reflux may also refer to:

• Duodenogastric reflux or biliary reflux
• Acid indigestion, cardialgia or pyrosis, all synonyms for heartburn
• Acid reflux disease, gastric reflux disease or gastro-oesophageal reflux disease (GORD), all synonyms for gastroesophageal reflux disease (GERD)
• Atypical reflux, extraesophageal reflux disease (EERD), supraesophageal reflux or supra-esophageal reflux, all synonyms for laryngopharyngeal reflux (LPR)
• Vesicoureteral reflux (VUR)
• Superficial venous reflux, see Chronic venous insufficiency