Each category of taxonomic hierarchy refers to as a unit of ______.

Taxonomic hierarchy is the sequence of arrangements of taxonomic categories in a descending order during the classification of organisms. Each category of taxonomic hierarchy refers to as a unit of classification. Classification is the process by which anything is grouped into convenient categories based on some easily observable characters. Systematics (term coined by Linnaeus) is the study of historical relationships of groups of biological organisms. Nomenclature is giving distinct scientific names to various structures including living organisms for their identification.