Nomenclature is "assigning the names to the organisms".Names are not common name because they are not acceptable all over the world.Like plant Gurhal in Hindi is also called China rose in English,Padmacharini in Sanskrit,Jaswand in Marathi and so on.
so, the nomenclatue helps in giving the scientific names so that the species can be organised all over the world.Practices of providing names to the organisms are :
(a) Polynominal nomenclature : Before 1750,scholars desired to designate a particular species usually added a series of descriptive words.For example,the scientific name of Caryophyllum is Caryophyllum sexatiles foils granineus umbellatis corymbis.Meaning Caryophyllum growing on rocks having grass like leaves as well as umbrella corymb arrangement of flowers.So the names become lengthy to remember.
(b) Binomial nomenclature : According to this system,the name of a organism had two words,the first is genus and the second is species.e.g.,Pisum sativum (pea).
(c) Trinomial nomenclature : Sometimes three words are used for the name which are generic,specific and subspecific.Homo sapiens for modern man.