Gastric acid, primarily composed of hydrochloric acid, is a digestive fluid produced by the stomach. It plays a crucial role in breaking down food, activating digestive enzymes, and providing an acidic environment that helps kill harmful bacteria. The production of gastric acid is stimulated by the presence of food in the stomach and is regulated by hormones and nerve signals. While it aids digestion, excessive gastric acid can lead to conditions like acid reflux or gastritis, which may require medical attention.