Back in olden times, irons (we'll stick with irons in our examples) were muscleback blades with thin and small clubfaces and mass concentrated behind the sweetspot. Hit the ball off-center with one of these irons and you'd feel it in your hands (ouch!) and see the results in a very poor golf shot.
The concept of "forgiveness" in golf clubs entered the sport when Karsten Solheim, Ping's founder, began marketing perimeter-weighted irons. These clubs moved mass to the perimeter of the iron head, which had the effect of lessening the bad results from off-center strikes.
Clubs that offer lots of forgiveness are classified as game-improvement clubs. Other design elements that clubs with lots of forgiveness may offer are larger clubheads and clubfaces, cavity backs, thicker toplines and wider soles, more weight lower and deeper in the clubhead, offset, and (in woods) slightly closed faces. High MOI and low center of gravity are what game-improvement clubs target, with forgiveness the goal.
Why "forgiveness"? Because these designs elements forgive the golfer for some of his mistakes.
Does forgiveness make bad shots go away? No. Improving your swing, making better contact with the ball, is the only way to make bad shots rare. But forgiveness can make that slice a little less severe; it can make a shot struck off-center travel almost as far as one with perfect contact; it can help get a ball a little higher in the air.
Forgiveness in clubs helps the golfer by making his bad shots just a little less bad.
