A landrace is a local variety of a domesticated animal or plant species which has developed largely by natural processes, by adaptation to the natural and cultural environment in which it lives. It differs from a formal breed which has been selectively bred deliberately to conform to a particular formal, purebreed standard of traits. Landraces are usually more genetically and physically diverse than formal breeds. Many formal breeds originated from attempts to make landraces more consistent, and sometimes a particular type has both landrace and formal breed populations. Sometimes a formalised breed retains a landrace name, despite no longer being a true landrace. When an animal landrace is codified as a pedigree breed without significant selective breeding to alter it, it is often referred to as a natural breed or traditional breed by breeder and fancier organisations. Similarly, the term traditional variety is sometimes applied to plant landraces.
Landraces are distinct from ancestral species of modern stock, and from separate species or subspecies derived from the same ancestor as modern domestic stock. Landraces are not all derived from ancient stock unmodified by human breeding interests. In a number of cases, most commonly dogs, domestic animals have reverted to "wild" status by escaping in sufficient numbers in an area to breed feral populations that, through evolutionary pressure, form new landraces in only a few centuries. Modern plant cultivars can also fairly quickly produce new landraces through undirected breeding.