Race: A race is an informal taxonomic rank below the level of species. It is used as a higher rank than the strain with several strains making up the race. Races may be distinct phenotypic populations within the same species or they may be defined in other ways. Example: Caucasoid, Mongoloid and Negroid races of Modern man.
Breed: Breed is a morpho physiological distinct subgroup of a race where crossing normally occurs within the sub group in order to maintain its distinct identity. Example: Rhode Island Red, Plymouth Red, Leghorn of poultry.
Cultivar: Is a group of plants selected for desirable characters that can be maintained by propagation. Most cultivars arisen in cultivation but a few are special selection from the wild. Example: Ornamental plants like roses, camellias, daffodils are cultivars produced by careful breeding and selection for flower colour and form.
Variety: It is a major subdivision of species that has distinct morpho physiology and genetic makeup giving it a unique adaptability. Example: Cauliflower , cabbage . The term variety is equivalent to the term sub species in ecology.