University
A University is an institution of post-secondary education, usually meaning one that has many colleges under its auspices. There is, however, no rule that this must be the case for a school to use the word university in its name. True universities will often not only have many distinct undergraduate colleges, but usually several prominent graduate schools. Graduate schools offer advanced degrees in many academic fields, and sometimes also offer professional degrees in fields like Medicine and Law.
The most prominent universities are the older colleges that have grown over the centuries since their founding, and the land grant State universities which were founded to make higher education affordable for the common man (and, eventually, woman).