Taxonomy is the science of classification. It comes from the Greek taxis meaning arrangement or division and nomos meaning law. It provides a conceptual framework for discussion, analysis, or information retrieval. It arranges hierarchically, elements of a group (taxon) into subgroups (taxa) that are mutually exclusive. Each group has the same properties, behaviours, and constraints. And each increasing level has further properties, behaviours, and constraints.
In biological terms this would be the classification of species.