A fox is a representative of the dog family (Canidae). In German usage, this usually means the red fox, more generally the genus group of the true foxes. The word fox has its origin in the Middle High German term vuhs for the male red fox (Canis vulpes). The related vocabulary fuhs (Old High German), vos (Dutch) and fox (English) are synonymous. The feminine form of the word changed from Old High German voha to Middle High German vohe, Gothic faúho, and Old Icelandic foa. The word Fähe, which in hunter and biologist language refers to female red foxes in particular and female canids in general, also has its origin in the Old High German feminine form.

The totality of species trivially referred to as "foxes" is not a closed descent community (clade), but a group of more or less closely related species and genera of dogs, which through convergent evolution resemble each other externally to a greater or lesser extent (polyphyly). The similarities of all these taxa are, however, exhausted in a rather small growth, mostly rather short legs and a bushy tail. Many, especially tropical representatives are also characterized by relatively large ears. Traditionally, species referred to as "foxes" are found in two genus groups of the dog family: the true foxes (Vulpini) and their sister group, the true dogs (Canini).

According to current kinship analyses based on DNA comparisons, these traditionally held generic groups are also not closed ancestral communities. Instead, the "foxes" are distributed among three clades: a gray fox clade, a red fox clade, and a clade of exclusively South American wild dogs.