A bunion, medically known as hallux abducto valgus (HAV) describes the bony bump at the big toe along the ball of the foot. This bump is actually the big toe joint (first metatarsophalangeal joint) that has been pushed out of place, and may also have had some extra growth around the joint.
Bunions get progressively worse over time, starting out as relatively flexible and mobile, and ultimately becoming rigid and permanent changes in the structure of the feet. This can make it very difficult to wear regular footwear, with the sides of the shoes rubbing against the protruding bunion and worsening the problem.