Indigestion, or dyspepsia, is a term given to a spectrum of causes that lead to pain or discomfort felt in the stomach, usually after eating. It could be due to several reasons, which include overeating, eating greasy foods or foods that disagree with you. Heartburn is a very specific symptom, characterized by a burning sensation in the chest due to the backflow or regurgitation of stomach acid and stomach contents. Heartburn may also be a symptom of indigestion. The main difference between indigestion and GERD is that GERD always involves a backflow of stomach acid, but in indigestion, there may or may not be stomach acid reflux.