While taxonomy is the classification and naming of all living things, systematics refers to the study of the relationships between these living things as they evolve. Taxonomic hierarchy was devised and published by Swedish scientist Carl Linne in 1735. All branches of systematics, such as botany, zoology, microbiology and mycology, are covered under taxonomy. Taxonomy as the science of biological classification is a subdivision of systematics.
All known living organisms are classified and named using a set of universally agreeable rules and system called binomial nomenclature. The hierarchy of biological classification is composed of eight major taxonomic levels. They are: domain, kingdom, phylum, class, order, family, genus and species in that order. Common names are those used in everyday life, but the scientific names are not frequently used by the layman. They are usually composed of two names, where the first letter of the first name has to be capitalized. For example, the pet commonly known as a dog is scientifically called Canis familiarus.
While a lion is called Panthera leo, horse is Eqqus caballus, crocodile is Crocodilis niloticus, cat is Felis catus, and a giraffe is Giraffa camalopardalis. On the other hand, onion is Allium cepa, potato is Solanum tubersum while spinach is Lactuca sativa. Scientific names should always be italicized.