Taxon: A level of biological classification is called a taxon, e.g. phylum, order, family, etc. Taxonomic Hierarchy: In taxonomy, different taxa have their own different levels. This means that a particular taxon will come only after another particular taxon. For example; species always comes after the genus and it can never be the other way around. 

Flow Chart of Plant Categories
Kingdom →Division →Order →Family →Genus →Species
Flow Chart of Animal Categories
Kingdom →Phylum →Order →Family →Genus →Species
In Some cases, animals or plants are further classified into sub-groups; like super-class,
class or sub-phylum.
When we go up the taxonomic hierarchy; the number of common characters becomes lesser and lesser. For example; all members of a species will have the maximum number of common characters. On the other hand, all members of a genus will have a lesser number of common characters.
The number of individuals increases as we go up the taxonomical hierarchy.