Rudimentary limb

Polydactyly or polydactylism (from Greek πολύς (polys) 'many', and δάκτυλος (daktylos) 'finger'), also known as hyperdactyly, is an anomaly in humans and animals resulting in supernumerary fingers and/or toes. Polydactyly is the opposite of oligodactyly (fewer fingers or toes). [Source: Wikipedia ]

Synonyms
Hypoplasia of all skeletal structures of a limb
Is A
Limb reduction
Hypoplasia of all skeletal structures of a limb