Classification is a process in which closely resembling organisms are placed in a group. The groups which have similarities are placed into larger groups. The various grouping levels or ranks in classification are known as taxonomic categories.
Each category is referred to as a unit of classification or rank and is commonly called taxon. A taxon is a general term for grouping in a systematic classification. A taxon refers to a group of similar and genetically related individuals having certain characters different from other groups. For example, all the insects form taxonomy as they have some common characters which are different from other groups.The category is an abstract term that simply represents a rank or a level. Taxon represents a biological object and is assigned to a category. For example, taxon of birds is aves and the category is class. Taxonomy of sponges is peripheral and the category is phylum. On classifying an organism in a particular taxon, we should have basic knowledge of characters of the individual group.