A breed is a specific group of domestic animals having homogeneous appearance (phenotype), homogeneous behavior, and/or other characteristics that distinguish it from other organisms of the same species. Breeds are formed through genetic isolation and either natural adaptation to the environment or selective breeding, or a combination of the two. Despite the centrality of the idea of "breeds" to animal husbandry and agriculture, no single, scientifically accepted definition of the term exists. A breed is therefore not an objective or biologically verifiable classification but is instead a term of art amongst groups of breeders who share a consensus around what qualities make some members of a given species members of a nameable subset.
When bred together, individuals of the same breed pass on these predictable traits to their offspring, and this ability – known as "breeding true" – is a requirement for a breed. Plant breeds are more commonly known as cultivars. The offspring produced as a result of breeding animals of one breed with other animals of another breed are known as crossbreeds or mixed breeds. Crosses between animal or plant variants above the level of breed/cultivar (i.e. between species, subspecies, botanical variety, even different genera) are referred to as hybrids.
The breeder (or group of breeders) who initially establish a breed, do so by selecting individual animals from within a gene pool that they see as having the necessary qualities needed to enhance the breed model they are aiming for. These animals are referred to as "breed foundation", or "breed origination". Further, the breeder mates the most desirable from his point of view representatives, aiming to pass such characteristics to their progeny. This process is known as selective breeding (also called artificial selection). A written description of desirable and undesirable breed representatives is referred to as a breed standard. Breed standards may vary from association to association, and may also change over time. A licensed breeder will frequently have their animals checked by such associations in order to ensure that they continue to meet the breed standard.
Breed specific characteristics also known as breed traits are inherited, and purebred animals pass such traits from generation to generation. Thus, all specimens of the same breed carry several genetic characteristics of the original foundation animal(s). In order to maintain the breed, a breeder would select those animals with the most desirable traits, to achieve further maintenance and developing of such traits. At the same time, avoiding animals carrying characteristics, not typical and/or undesirable for the breed, known as faults or genetic defects. The population within the same breed consists of a sufficient number of animals to maintain the breed within the specified parameters without the necessity of forced inbreeding. The breed includes several bloodlines that can be interbred to sustain the breed in whole without weakening the gene pool.
Domestic animal breeds commonly differ from country to country, and from nation to nation. Breeds originating in a certain country are known as "native breeds" of that country.