Dog is the common use term that refers to members of the subspecies Canis lupus familiaris. The term is sometimes used to refer to a wider range of species: it can be used to refer to any mammal belonging to the family Canidae, which includes wolves, foxes, jackals, and coyotes; it can be used to refer to the subfamily of Caninae, or the genus Canis, also often called the "true dogs".[7] Some members of the family have "dog" in their common names, such as the Raccoon Dog and the African Wild Dog. A few animals have "dog" in their common names but are not canids, such as the prairie dog and the dog fish.

The English word dog comes from Middle English dogge, from Old English docga, a "powerful dog breed".[8] The term may derive from Proto-Germanic *dukkōn, represented in Old English finger-docce ("finger-muscle").[9] The word also shows the familiar petname diminutive -ga also seen in frogga "frog", picga "pig", stagga "stag", wicga "beetle, worm", among others.[10] Due to the archaic structure of the word, the term dog may ultimately derive from the earliest layer of Proto-Indo-European vocabulary, reflecting the role of the dog as the earliest domesticated animal.[11]

Dog ousted traditional English hound by the 16th century, before which time it had the meaning of "dog" rather than modern "hunting dog", as in other Germanic languages – it is cognate to German Hund, Dutch hond, common Scandinavian hund, and Icelandic hundur. Hound itself is derived from the Proto-Indo-European *kwon- "dog", found in Welsh ci (plural cwn), Latin canis, Greek kýōn, Lithuanian šuõ, just to name a few.[12]

In breeding circles, a male canine is referred to as a dog, while a female is called a bitch. A group of offspring is a litter. The father of a litter is called the sire, and the mother is called the dam. Offspring are generally called pups or puppies until they are about a year old. The process of birth is whelping.[13]