Final answer:
Heartburn is the term for the sensation caused by stomach acid backing up into the esophagus. It occurs due to a malfunctioning gastro-esophageal sphincter and can lead to a chronic condition known as GERD.
Step-by-step explanation:
The medical term that refers to the condition where stomach contents back up into the esophagus resulting in a burning sensation is known as heartburn. This uncomfortable sensation occurs when there is a failure of the gastro-esophageal sphincter (or cardiac sphincter) to remain completely closed. This sphincter normally prevents the contents of the stomach from entering the esophagus, and when it malfunctions, acidic digestive juices can escape, leading to the tell-tale burning sensation. People who frequently experience heartburn may be diagnosed with gastroesophageal reflux disease (GERD), a more chronic form of this acid reflux condition.