Mouth ulcer. Basically just a small open wound in your mouth that hurts like hell.
canker sores suck.....
by Bobby De Niro October 30, 2005
A canker sore is a sore on the inside of your mouth that you typically can't ignore, It suck ass
Lisa's a total slut no wonder she ended up with a canker sore.
by shanedashiz July 29, 2010