Utility dog refers to a dog originally bred for a specific working purpose that is no longer applicable today or those that do not belong to any category.
In the UK, specifically under The Kennel Club, these dogs are registered in the Utility Group category, a grouping of dog breeds that do not fit in any of the other categories. In other kennel clubs such as in New Zealand and Australia, utility dogs still refer to guard dogs, rescue dogs and messenger dogs, while others do not use this category at all. Kennel clubs in America and Canada refer to a group of dogs in the utility category as Working Group, which also includes dog breeds under the Pastoral or Herding Group.
Most often people mistake the utility dogs for unrecognised dog breeds. These two are entirely different. In The Kennel Club, utility dogs are dogs that do not fit any categories or has outgrown their purpose, whereas unrecognised dogs are breeds with no sufficient verifiable information to develop breed standards, judging protocols and breeding programmes.