A bunion is a prominence on the inner side of the foot at the base of the big toe. The bunion usually forms because of a problem with the alignment of the bones of the forefoot. This causes pressure and prominence of the base of the big toe. Irritation of the soft tissues surrounding this part of the foot causes further swelling and pain.
What Can be Done About your Bunion by Daniel W. Bienkowski, MD.
More on Bunions from the American Academy of Orthopedic Surgeons (AAOS).