A taxon (plural taxa) is an element of a taxonomy, e.g. in the scientific classification in biology. Taxa form a hierarchical scheme, each being broken down into subtaxa.
In traditional Linnaean taxonomy, taxa are ranked as follows, with some of the less widely used ranks indented:
A prefix is used to indicate a ranking that falls between two taxa. The prefix super- indicates a rank above another, the prefix sub- indicates a rank below another, and the prefix infra- indicates a rank below sub-. For instance:
Superclass
Class
Subclass
Infraclass
It has become generally accepted that taxa should contain an ancestral form and all or some of its descendants, though the validity of the latter category is increasingly debated.
