noun.
That division of the natural sciences which treats of the classification of animals and plants, primarily by consideration of their natural relationships with respect to their structure or genetic origin; the laws or principles of classification; systematics.
noun.
A systematic arrangement of objects or concepts showing the relations between them, especially one including a hierarchical arrangement of types in which categories of objects are classified as subtypes of more abstract categories, starting from one or a small number of top categories, and descending to more specific types through an arbitrary number of levels. An ontology usually contains a taxonomy as one of the important principles of organization.