noun. 1. With regard to biological taxonomy, a sub-class of a species consisting of those members of the species which are separate with reference to specific minor traits which do not impact their capacity to interbreed to produce fertile offspring. The different breeds of domestic animals are instances of options. 2. With regard to language, a rendition of a language which is phonologically or grammatically independent from the principle language and might be correlated with such categories as general area, ethnicity, or social class.