1. Allopatric species : The species inhabiting different geographical area.
  2. Analogus species : This refers to the species inhabiting different geographical regions.
  3. Biochemical systematics : The classification of plants and animals on the basis of biochemical characteristic is called biochemical systematic.
  4. Category : Plants and animals are ranked in a hierarchy of categories such as kingdom, phylum (for animal) division (for plants) class, order, family, genus and species. Both in plants and animals, phylum and species are the highest and the lowest categories respectively.
  5. Chemotaxonomy : The classification of living organisms on the basis of bio-chemical characteristics is called Chemotaxonomy.
  6. Evolutionary species : These are the linkages evolving on altogether different lines from one another.
  7. Experimental taxonomy : It is identification of evolutionary units with species by experimentally determining their genetical interrelationship and the role of environment in their formation.
  8. Family : A number of genera having several common characters constitute a family.
  9. Genetic species : These are groups of interbreeding populations which are productively isolated from one another.
  10. Hierarchy : It is a system of arrangement or a framework for classification in which taxonomic categories are placed in order of logical sequence.
  11. Hinney : Sterile hybrid obtained from male horse and female donkey.
  12. Homology : Relationship of comparable structures in different organisms.
  13. Key : It provides an easy way for identifying an organism by making use of diagnostic or distinguishing characters.
  14. Kingdom : It is the highest taxonomic category. All the animals are included in Kingdom Animallia while all plants are included in the Plant Kingdom.
  15. Mule : Sterile hybrid obtained from female horse and male donkey.
  16. Numerical taxonomy : Use of statistical method in taxonomy is termed as numerical taxonomy.
  17. Order : A number of families having many common characters are placed in order.
  18. Phylum : A number of classes having common features constitute a phylum.
  19. Species : A group of organisms which resemble each other structurally as well as physiologically and interbreed amongst themselves to produce the young ones of their own type.
  20. Taxon : Taxon is also defined as a unit of classification of organisms which can be recognized to a definite category at any level of classification.