There are different types of ADHD. The inattentive type, where the kid just isn't focused and acts like a space cadet, the combined type, where they aren't focused and also hyper, and the impulsive type where the main problem is the impulsivity or hyperactivity. So a kid with inattentive type ADHD will look completely different than one with hyperactive/impulsive type, but they are all still called ADHD. ADD used to be the inattentive type but now it's categorized as ADHD--inattentive type. Wikipedia has a good ADHD page.
