Dwarf is a specific definition used to describe animals or plants with particular genetic characteristics and disorders. A dwarf is not just a small variety of an animal, although in some instances the word is used casually this way. A true dwarf animal, like a dwarf person, has genetic disorders of cartilage and/or bone development. Dwarves are not bred to produce miniatures.
Dwarf Animals In animals the most common form of dwarfism is achondroplasia, which produces markedly short limbs, increased spinal curvature, and distortion of skull growth. This dwarfism appears in miniature horse and cattle breeds if their parents have dwarf genes.
Dwarfism results in animals with abnormalities which may cause serious breathing and mobility problems. No reputable breeder will knowingly breed animals known to have a dwarfing gene.
Some animals and plants were historically given the name dwarf when the condition was understood to mean simply small. Dwarf rabbit breeds are not true genetic dwarfs, and do not have medical problems due to their condition or limited size. The same is true of dwarf or pygmy goats.
Dwarfism in Plants Dwarfs are often produced by grafting a normal plant onto a dwarfing rootstock, which limits the amount of nutrition received by the normal plant and thus restricts its growth.
Dwarfism in plants affects mainly the plant's size, although it may also influence how they utilize nutrients.
Some plants are known to be environmental dwarfs. In the arctic, plants grow as dwarfs to create a better environment for themselves, but they grow to a much larger size if moved to a more favorable habitat.
As dwarfism is a genetic mutation, you cannot correctly describe a Bonsai as a dwarf tree. A Bonsai, like a dwarf apple, will produce seeds that have normal sized offspring. Bonsai size is determined by cultural conditions.