Real Dictionary

ulcer
countable noun: An ulcer is a sore area on the outside or inside of your body which is very painful and may bleed or produce an unpleasant poisonous substance.

ulcer in American English
an open sore (other than a wound) on the skin or some mucous membrane, as the lining of the stomach ( peptic ulcer), characterized by the disintegration of the tissue and, often, the discharge of pus
noun: a sore on the skin or a mucous membrane, accompanied by the disintegration of tissue, the formation of pus, etc

ulcer in British English
noun: a disintegration of the surface of the skin or a mucous membrane resulting in an open sore that heals very slowly