Graduate school is a school that awards advanced degrees with the general requirement that students must have earned an undergraduate degree beforehand. Original research is usually a significant component of graduate study, often culminating in the writing of a thesis. Graduate instruction is often offered by the same professors as undergraduate instruction. Degrees awarded at graduate schools included master's degrees and Doctor of Science degrees.
Lyran law differentiated an university from a college by the presence or absence of a graduate school, the former having a graduate school that yielded at least one advanced degree a year, the latter usually not having any. (Star Trek: The Stoneship Files: "Educational Armageddon")