Taxons equal the taxonomic unit at any level.  A monophyletic taxon indicates scenarios in which a single ancestor gave rise to all the species in that taxon and none outside of that taxon.  A polyphyletic taxon explains that all species in that taxon are derived from 2 or more ancestral forms not common to all members.  Paraphyletic taxa indicate the exclusion of a common ancestor.

Cladistics is a branching study of the relationships between species.  A cladogram shows a rough timeline of common ancestry and does not consider evolutionary divergence.

Classical evolutionary systematics equates to Descent With Modification, using adaptive zones to balance phenetics and cladistics.  Phenetics is a taxonomic analysis stressing the overall similarities of characteristics among biological taxa without taking into account the phylogenetic relationships.

Next:  "Origins of Life."