What kind of jobs do the software engineers who earn $500K a year do?
aminariana.com
aminariana.com
http://www.investopedia.com/terms/e/economicrent.asp
The definition is not that good, and the piece goes on to refine all rents as due to imperfectly competitive markets, (which is a bit nauseating - "Elvis markets" happen regardless of competition - substition breaks down, etc...).
But it is a start.