Based on this paragraph about dogs, what is a companion dog?

A companion dog is a dog that does not work, providing only companionship as a pet, rather than usefulness by doing specific tasks. Many of the toy dog breeds are used only for the pleasure of their company, not as workers. Any dog can be a companion dog, and many working types such as retrievers are enjoyed primarily for their friendly nature as a family pet, as are mixed breed dogs. The American Kennel Club also offers a Companion dog title for judged dog obedience competitions.

A companion dog is a dog that provides only companionship as a pet, rather than usefulness by doing specific tasks.