The Breed Standard is the set of guidelines used to ensure that the animals produced by a breeder conform to the specifics of the breed.  Breed standards are created by breed associations to reflect the ideal animal fit for the function it was bred for  (i.e., mousing/ratting, herding, companion, etc.).

Breed standards are not scientific documents, and  some standards may vary from association to association, and from country to country, even for the same species and breed. There is no one format for breed standards across all species, and breed standards do change and are updated over time. 

Within the Danish-Swedish Farmdog breeding community, both in the US and abroad, one breed Standard is recognized as the accepted standard -- the Federation Cynologique Internationale (FCI) accepted standard.  However, there is on exception currently -- the United Kennel Club has adopted a slightly different breed standard due to their club regulations.