in garden nursery, & confir cultivar collecter circles, which is not bonsai per say, dwarf is usually used to denote a cultivar with a much slower growth rate than the wild type form of a species. Generally dwarf conifers grow less than 8 inches per year. Miniature conifer cultivars grow less than 4 inches per year. Usually these are chance genetic mutations, selected from wild trees, or witches brooms, or chance seedlings spotted at nurseries. Not enough money in landscape plants for much genetic enginering to have been done yet. As costs of producing GMO's come down I supose transgenetic trees will become more common. For the moment almost all are natural chance mutations. So dwarf and miniature are terms from the nursery trade.