Sore, canker: A small ulcer crater in the lining of the mouth that is often painful and very sensitive. Also known as an aphthous ulcer.
Canker sores are one of the most common problems that occur in the mouth. About 20% of the population (1 in 5 people) have canker sores at any given time. Canker sores typically last for 10-14 days and they heal without leaving a scar.
|Picture of a canker sore|