Prep is short for prepatory and prepatory means to prepare so a prepatory school means that that school prepares the students for high school/college and life.
But there's a LOT more.
The most famous ones/best ones are filled with kids who can really THINK. you are put into an environment that includes every one, and you aren't afraid that you'll be "too smart" because every body is intelligent and intellectual (well, most). what they teach goes up and beyond what you would get at an average high school.
Most also have an extensive extracurricular program (not academic stuff), like sports and the arts.
They're basically trying to prepare you for the colleges that you will be looking for if you go to a good prep school (like Ivy-leagues etc.)
Toronto Prep School was created in 2009.
Copthorne Prep School was created in 1902.
Elppin Prep School was created in 1992.
the top prep school is probably Harvard then Yale
Cedar Hill Prep School was created in 2003.
Prep School - 2014 was released on: USA: 2014
menefesto of a prep prefect
Prep School - 1926 was released on: USA: 18 January 1926
Poly Prep Country Day School was created in 1854.
The Prep School Negro - 2012 was released on: USA: 2012
The cast of Prep School - 1926 includes: Arthur Lake
I don't think a prep school would feel you were a contribution to their school if you had to repeat a grade...