What are called systematic categories? why is the modern classification called natural?

Taxonomy (or classification) is a discipline that is part of the science of biology. The purpose of taxonomy is to combine different organisms into different taxonomic groups based on the degree of their relationship, common characteristics, etc. The classification is called natural for the reason that it is not invented, but only reflects the division that occurred during evolutionary development. Classification begins with the smallest taxon – a biological species, and then moves on to larger associations.