Google hasn't been very helpful on this one and my textbook once again assumes we are born with certain knowledge as it doesn't delve any further than, "Many practical engineering problems involve systems acted on by impulsive forcing terms" without further explanation. Isn't that nice... So the question is; what is this? My guess is it has something to do with a force on a system for a given time (impulse) and how it is represented as some 'term' to the function itself. Is that about right?