An ulcer on the foot is an open wound on the foot.  If you examine your feet and see an open wound, or a piece of hard skin, or a blister, or an area of redness, please have it checked right away.  If it is open, then it is considered an ulcer and you are in danger for further complications such as an infection, which if not treated, may travel to the bone.  Long standing ulcers that do not heal sometimes go on to need surgical intervention, IV antibiotics, and even amputation if not treated.  If you have an open wound that you think may be an ulcer, please have it checked right away.