What is Pathology - What exactly is an ulcer?

What is Pathology - What exactly is an ulcer?
​ Inflammation-induced necrosis of the superficial layers of the implicated organ causes an ulcer, which is a defect in the surface lining of the skin or mucosae. The activity of hydrochloric acid and pepsin in the digestive juices causes mucosal necrosis in gastric or duodenal ulcers. The lytic action of amoebas in the lumen causes ulcers in amebic colitis. The cause of ulcerative colitis's confluent ulcerations of the large intestine is unknown.