
A shank is defined as a shot that is contacted by the hosel of the club, rather than the club face. The hosel is the portion of the club where the shaft connects to the club head, and when it strikes the ball, your shot will usually shoot directly off to the right (for a right handed golfer).
It is almost impossible to wind up with a success shot when you hit a shank, and many of your shanks will result in a lost ball and a penalty. While golfers find all sorts of different ways to hit poor shots, very few shots are as damaging as the shank.