Book smarts vs. common sense - Intelligence thunderdome.

[Arthur Dent]

You've obviously never spent any time around a tech school. I've know people who could do highly advanced math in their sleep and quote any theorem from any science class they ever took. but ask them how to put an airconditioner in a window or how to deal with some everyday situation, and they are completely lost.

To me, "common sense" is the ability to evaluate a situation and come up with a way to deal with that situation without any special training or experience. The ability to see A and B and figure out C. Like figuring out how to fix a loose door hinge by sticking toothpicks in the screw holes before putting the screws back in, or something like that.