The tortrix moth genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

Coccyx is nowadays considered a junior synonym of Cydia.

The coccyx (icon ; plural
In linguistics, plurality or [a] plural is a concept of quantity representing a value of more-than-one. Typically applied to nouns, a plural word or marker is used to distinguish a value other than the default quantity of a noun, which is typically one...

: coccyges), commonly referred to as the tailbone, is the final segment of the vertebral column. Comprising three to five separate or fused vertebrae (the coccygeal vertebrae) below the sacrum
In vertebrate anatomy the sacrum is a large, triangular bone at the base of the spine and at the upper and back part of the pelvic cavity, where it is inserted like a wedge between the two hip bones. Its upper part connects with the last lumbar vertebra, and bottom part with the coccyx...

, it is attached to the sacrum by a fibrocartilaginous joint
A joint is the location at which two or more bones make contact. They are constructed to allow movement and provide mechanical support, and are classified structurally and functionally.-Classification:...

, the sacrococcygeal symphysis, which permits limited movement between the sacrum and the coccyx.

The term coccyx comes originally from the Greek
Greek language
Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...

 κόκκυξ and means "cuckoo", referring to the curved shape of a cuckoo
The cuckoos are a family, Cuculidae, of near passerine birds. The order Cuculiformes, in addition to the cuckoos, also includes the turacos . Some zoologists and taxonomists have also included the unique Hoatzin in the Cuculiformes, but its taxonomy remains in dispute...

's beak when viewed from the side.
It is believed that in humans and other tailless primates (e.g.