A bunion (hallux valgus) is a sometimes painful structural deformity of the bones and the joint between the foot and big toe.

A bunion is an enlargement of bone or tissue around the joint at the base of the big toe (metatarsophalangeal joint). The big toe may turn in toward the second toe (displacement), and the tissues surrounding the joint may be swollen and tender.

Today the term usually is used to refer to the pathological bump on the side of the great toe joint. The bump is the swollen bursal sac and/or an osseous (bony) deformity that has grown on the mesophalangeal joint (where the first metatarsal bone and hallux meet).

The term “hallux valgus” or “hallux abducto valgus” are the most commonly-used medical terms associated with a bunion deformity, where “hallux” refers to the great toe, “valgus” refers to the abnormal rotation of the great toe commonly associated with bunion deformities, and “abducto” refers to the abnormal drifting or inward leaning of the great toe towards the second toe, which is also commonly associated with bunion disorders.