As I know it, and it is the system here.... A University is the global name for a collection of colleges and Schools (Not primary or high schools) but professional schools like law or medicine.
For example I work at a University, there are 5 colleges (Engineering, Science, Business, Arts and Education). There is also one school - The school of law. The colleges are then broken down onto different departments ie
College of arts is made up of history, philosophy, languages, etc
A School in the higher education sense does not contain different departments within it, rather they are global, with different specialisations within each.