An ulcer is a crater-like lesion on the skin or mucous membrane of the mouth, stomach, and other body areas.
Ulcers can be caused by inflammation or infection. Some ulcers may be caused by a cancer.
Habif TM. Principles of diagnosis and anatomy. In: Habif TP, ed. Clinical Dermatology. 5th ed. Philadelphia, Pa: Mosby Elsevier; 2009:chap 1.