Ulcer, gastric: A hole in the lining of the stomach corroded by the acidic digestive juices which are secreted by the stomach cells. Ulcer formation is related to H. pyloridus bacteria in the stomach, anti-inflammatory medications, and smoking cigarettes. Ulcer pain may not correlate with the presence or severity of ulceration. Diagnosis is made with barium x-ray or endoscopy. Complications of ulcers include bleeding, perforation, and blockage of the stomach (gastric obstruction).