What is Systematics, phylogeny, cladistics?

Systematics is the study of the diversity of organisms and of the relationships among them; a phylogeny is the tree of those relationships, a hypothesis about the order in which lineages split. Phenetics groups organisms by overall similarity, counting all characters equally; cladistics groups them by shared derived characters only, so that every group is a clade — an ancestor and all of its descendants. Modern classification aims to make every named taxon a clade.