Hallux varus, or sandal gap,[1] is a deformity of the great toe joint where the hallux is deviated medially (towards the midline of the body) away from the first metatarsal bone. The hallux usually moves in the transverse plane. Unlike hallux valgus, also known as hallux abducto valgus or bunion, hallux varus is uncommon in the West but it is common in cultures where the population remains unshod.
https://en.wikipedia.org/wiki/Hallux_varus

Hallux varus is a clinical condition characterized by medial deviation of the great toe at metatarsophalangeal (MTP) joint. This condition may present with varying degrees of severity, causes, and symptoms. Adult acquired hallux varus deformity is commonly iatrogenic, commonly resulting from surgery for hallux valgus. (1,2,3)
A patient may have difficulty in walking and wearing shoes. Mild hallux varus can be managed with stretching exercises and splints. However, if the symptoms become significant and affect daily activities, then surgery should be considered.[1][2]

Etiology

Rarely, hallux varus is congenital. Flexible hallux varus may be found in newborns and reflects their intrauterine positioning. It corrects to valgus in early childhood when walking begins.[3]
More frequently this deformity develops after a surgical procedure for hallux valgus because of overcorrection, excessive lateral release, over-resection of medial eminence, over-plication of the medial capsule, zero-degree or negative intermetatarsal angle, or immobilization of the toe in excessive varus after surgery. Other causes include trauma and certain systemic inflammatory diseases such as psoriasis and rheumatoid arthritis.
https://www.ncbi.nlm.nih.gov/books/NBK470261/