System of naming organisms in which each organism is indicated by two words, the genus (capitalized) and species (lowercase) names, both written in italics.
For example, the tea rose is Rosa odorata ; the common horse is Equus caballus . The system was developed by Carolus Linnaeus in the mid 18th century. The number of binomial names proliferated as new species were established and more categories were formed, and by the late 19th century the nomenclature of many groups of organisms was confused. International committees in the fields of zoology, botany, bacteriology, and virology have since established rules to clarify the situation. See also taxonomy .