Taxonomy (from Greek: τάξις taxis "arrangement" and Greek: νομία nomia "method") is the practice and science of classification. Taxonomy uses taxonomic units, known as taxa (singular taxon). In addition, the word is also used as a count noun: a taxonomy, or taxonomic scheme, is a particular classification ("the taxonomy of ..."), arranged in a hierarchical structure. Typically this is organized by supertype-subtype relationships, also called generalization-specialization relationships, or less formally, parent-child relationships. In such an inheritance relationship, the subtype by definition has the same properties, behaviors, and constraints as the supertype plus one or more additional properties, behaviors, or constraints. For example: car is a subtype of vehicle, so any car is also a vehicle, but not every vehicle is a car. Therefore a type needs to satisfy more constraints to be a car than to be a vehicle.
Theoretical taxonomy - is classifying that which is only theorised about
Historcal taxonomy- is that which is classified by where it sits in history
Visual taxonomy - that which is classified by visually comparing to other things