Gastric outlet obstruction: Any disease that mechanically impedes gastric emptying, the normal emptying of the stomach. There is obstruction of the channel of the pylorus and duodenum through which the stomach empties. The cause of the obstruction may be a benign or malignant disease. The most common malignancy that produces gastric outflow obstruction is pancreatic cancer. The benign causes of gastric outflow obstruction include pyloric ulcer and gastric polyps in adults, pyloric stenosis and congenital duodenal webs in children, and the ingestion of caustic substances in all age ranges. Gastric outlet obstruction may be abbreviated GOO.