A subject within mathematics usually taught in final years of high school that's overused by the media, as of 2008, to describe any circumstance where various decisions would result in various outcomes (which is true for any decision simple or complex).
Most often used in the phrase "....the calculus of..."
Article title: "The Calculus of Union Strikes"
"What do Steven Chu and John Holdren have to say about the calculus of corn-based ethanol, and its impact on biodiversity in farm country" from the NY Times
"The calculus of reward and punishment in this world is surely more complex than sin equals cancer." from MSNBC