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A taxonomic class is a taxonomic rank conventionally below a taxonomic phylum and above a taxonomic order. A particular class is a taxon at that level. For example, Mammalia is the class of mammals, and Carnivora is one of its constituent orders.^[ref]

The hierarchy makes several statements simultaneously: an individual cat belongs to Mammalia, Carnivora and Felidae, at class, order and family ranks respectively. These nested memberships describe increasing specificity. They do not give three independent estimates of the cat's identity.

Consider a constructed sampling table with two classes, each represented by twelve sampled species. The first has two sampled orders containing six species each; the second has three containing four each. The class totals agree, while the within-class distribution differs. Class-level aggregation preserves the total and discards that structure. Nor would twelve sampled species establish twelve species in the complete class: sampling coverage is a separate issue.

A taxonomic class need not have a fixed number of orders, individuals or species. Its rank also does not specify a fixed age or a numerical amount of genetic divergence. Those are additional biological quantities or hypotheses that require evidence beyond the hierarchical label.

A taxonomic order is a taxonomic rank below a taxonomic class and above a taxonomic family. An order is a named grouping, or taxon, at that position in a classification. Its constituent families can themselves contain several genera and species.^[ref]

For example, Carnivora is an order containing the cat family Felidae. The order name and family name identify groups at different levels; the same animal belongs to both. This is nested classification rather than two competing identifications.^[ref]

A constructed database example illustrates the information lost during aggregation. Suppose an order contains three families with 2, 4 and 1 sampled species respectively. Reporting seven species for the order preserves the total but discards how those records were distributed among families. An analysis at order level can therefore conceal variation visible at family level.

The rank specifies hierarchical placement, not a fixed age, number of species or amount of genetic divergence. A phylogenetic tree instead expresses a hypothesis about ancestry and branching. Classification uses evolutionary evidence, but a rank label alone is not a numerical evolutionary distance.^[ref]

A taxonomic phylum is a major taxonomic rank conventionally below a taxonomic kingdom and above a taxonomic class. A particular phylum is a taxon at that rank. For example, chordates form the phylum containing Mammalia, which in turn contains orders such as Carnivora.^[ref]

The same animal can consequently belong to a phylum, a class and an order without these being competing identifications. Each level adds information about nested membership. The rank word phylum identifies a position in the hierarchy; the group name identifies which taxon occupies that position.

For a constructed survey example, suppose one phylum is represented by four sampled classes with 3, 7, 2 and 8 sampled species. Its total is $3+7+2+8=20$. A second phylum with two sampled classes containing ten species each has the same total. Reporting only twenty species for each phylum loses the class-level distribution, and neither count establishes the total diversity of the unsampled phylum.

A taxonomic rank does not itself specify a fixed age, number of constituent groups or numerical genetic distance. A phylogenetic tree addresses evolutionary relationships, while ranked names select particular groupings for classification.^[ref] The usefulness of the rank comes from organizing comparisons; the scientific interpretation still depends on what was sampled and the evidence supporting membership.