(1) The science of finding, describing, classifying, and naming organisms, including the studying of the relationships between taxa and the principles underlying such a classification.

(2) The classification of organisms in a hierarchical system or in taxonomic ranks (e.g. domain, kingdom, phylum or division, class, genus, species) based on shared characteristics or on phylogenetic relationships inferred from the fossil record or established by genetic analysis.

A taxon (plural: taxa) refers to any group or rank in a biological classification into which related organisms are classified. A taxonomic unit in the biological system of classification of organisms, for example: a phylum, order, family, genus, or species.

The image below shows the standard categories, or taxa, used to classify life, with the most specific category, species, at the top, and the most general category, domain, at the bottom.

The standard categories, or taxa, used to classify life.

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