Working dog

Detection dog of the Metropolitan Police patrolling in London
Guide dog in Brazil
Šarplaninac livestock guarding dogs at work in the Šar Mountains

A working dog is a dog used to perform practical tasks, as opposed to pet or companion dogs.

Definitions vary on what a working dog is: they are sometimes described as any dog trained for and employed in meaningful work; other times as any dog whose breed heritage or physical characteristics lend itself to working irrespective of an individual animal's training or employment; and other times again it is used as a synonym for herding dog.