One of the main objectives of Taxonomy is to assign organisms in the respective and correct placement of a systematic framework of classification. This framework is called the 'Taxonomic Hierarchy'. Typically, the taxonomic hierarchy uses some standard categories, like Kingdom, Phylum (or Division), Class, Order, Family, Genus, and Species. These categories are called Essential Categories. There may be sub-categories, like Super-family, Sub-species, etc. This categorisation is based on similarities and dissimilarities. When we go up in the hierarchy, similarities decreases.
Taxon (in Plural Taxa) is a taxonomic group or any real organism assigned to a given category. The taxon represents the rank or level of that organism. For example, Tiger is a taxon, Mangifera (Generic name of Mango) is a taxon.
The Category is also used in the taxonomic hierarchy. This represents a taxon.