Nordic walking uses two specially designed poles to work the upper body while walking. Similar to cross country skiing, the poles are used by the arms to match each step the person takes. Nordic walking increases your heart rate without increasing your rate of perceived exertion. While you can get a similar heart rate effect by walking faster, there are many people who do not want to walk faster or cannot walk fast. Nordic walking works the arms, shoulders and upper chest and back muscles through a full range of motion, stretching and lengthening those muscles which are often tight.
I really wish I could get into Nordic training... I tried it at my gym and it was like a bad sitcom! I fell off, I couldn't get coordinated. I seem to be able to exercise my arms or my legs, not both at once. I do know that skiers are built, though!