a painful sore in the mouth on either the cheeks or gums

a small sore in the mucuous membranes inside the mouth

a small, superficial, painful lesion of the mouth

Painful area of broken skin inside the mouth.

A mouth ulcer (from Latin ulcus) is the name for the appearance of an open sore inside the mouth caused by a break in the mucous membrane or the epithelium on the lips or surrounding the mouth. The types of mouth ulcers are diverse, with a multitude of associated causes including: physical or chemical trauma, infection from microorganisms or viruses, medical conditions or medications, cancerous and sometimes nonspecific processes. Once formed, the ulcer may be maintained by inflammation and/or secondary infection.