Actually, each term has a distinct meaning. Here is how they are different:
Heartburn is not a medical condition, but a symptom. It describes the mild to severe burning pain felt in the chest or throat when acid from the stomach seeps up into the esophagus. Heartburn pain can feel dull, sharp or tight, and it often moves up to the throat. Some people describe the pain as a feeling that something is lodged behind the breastbone.
Heartburn has nothing to do with your heart, but it can be mistaken for a heart attack because of the location of the pain. Over 60 million Americans experience heartburn at least monthly, and it usually occurs after a meal.
Acid reflux occurs when stomach acid flows back into the esophagus due to a weakening of the lower esophageal sphincter (LES). When functioning properly, the LES tightens to close the passage between the stomach and esophagus. If the muscle is weak or fails to tighten properly, gastric acid and digested food can back up into the esophagus.
Common symptoms of acid reflux may include cough, sore throat, sour taste in the mouth, and burning in the chest and throat.
Gastroesophageal Reflux Disease (GERD)
GERD is an acronym for gastroesophageal reflux disease. When acid reflux occurs more than twice per week, it can be diagnosed as GERD. Prolonged exposure to gastric acid creates inflammation and increases risk for esophageal tissue damage which can lead to cancer.
Symptoms of GERD can include heartburn, regurgitation, bad breath, damage to tooth enamel, dry cough, and difficulty swallowing.
If you are experiencing acid reflux on a regular basis, it is time to see a gastroenterologist (a physician with specialized training in diseases of the digestive tract). Antacids and H-2 blockers might offer temporary relief, and proton-pump inhibitors (PPIs) can reduce levels of stomach acid, but they should only be used for a 14-day treatment (source: AARP).