A taxon (plural: taxa)'s a group of (one or more) organisms, which a taxonomist adjudges to be a unit. Usually a taxon's given a name and a rank, although neither's a requirement. Defining what belongs or doesn't belong to such a taxonomic group's done by a taxonomist. It isn't uncommon for one taxonomist to disagree with another on what exactly belongs to a taxon, or on what exact criteria should be used for inclusion. Taxonomists sometimes make a distinction between "good" (or natural) taxa a… (More on Taxon)