The coat of the domestic dog (Canis lupus familiaris) refers to the hair

Hair

Hair is a filamentous biomaterial, that grows from follicles found in the dermis. Found exclusively in mammals, hair is one of the defining characteristics of the mammalian class....

 that covers its body. A dog's coat may be a double coat, made up of a soft undercoat and a coarser topcoat

Guard hair

Guard hairs are the longest, coarsest hairs in a mammal's coat, forming the topcoat . They taper to a point and protect the undercoat from the elements. They are often water repellent and stick out above the rest of the coat...

, or a single coat, which lacks an undercoat. The terms fur

Fur

Fur is a synonym for hair, used more in reference to non-human animals, usually mammals; particularly those with extensives body hair coverage. The term is sometimes used to refer to the body hair of an animal as a complete coat, also known as the "pelage". Fur is also used to refer to animal...

 and hair

Hair

Hair is a filamentous biomaterial, that grows from follicles found in the dermis. Found exclusively in mammals, hair is one of the defining characteristics of the mammalian class....

 are often used interchangeably when describing a dog's coat, however in general, a double coat, e.g., like that of the Newfoundland

Newfoundland (dog)

The Newfoundland is a breed of large dog. Newfoundlands can be black, brown, gray, or black and white. They were originally bred and used as a working dog for fishermen in the Dominion of Newfoundland, now part of Canada. They are known for their giant size, tremendous strength, calm dispositions,...

 and most mountain dog

Mountain dog

Mountain dog is a generic form of canidae, dog, dog breed or landrace typically from mountain environs.They are often a working dog, particularly a livestock or flock guardian or farm dog. By and large, these dogs tend to have a claimed Molosser dog in their genetic heritage...

s, is referred to as a fur coat, while a single coat, like that of the Poodle

Poodle

The Poodle is a breed of dog. The poodle breed is found officially in toy, miniature, and standard sizes, with many coat colors. Originally bred as a type of water dog, the poodle is highly intelligent and skillful in many dog sports, including agility, obedience, tracking, and even herding...

, is referred to as a hair coat.
There is a greater variety of coat colours, patterns, lengths and textures found in the domestic dog than in its wolf

Subspecies of Canis lupus

Canis lupus has 39 subspecies currently described, including two subspecies of domestic dog, Canis lupus dingo and Canis lupus familiaris, and many subspecies of wolf throughout the Northern hemisphere...

 relations, even though dogs and wolves belong to the same species (Canis lupus).