Attention Deficit Disorder (with or without Hyperactivity) is a neurological condition (probably genetic in origin) where the sufferer has a very reduced ability to; maintain attention without distraction; control of doing, or saying something due to impulsivity and lack of appropriate fore-thought; and control the amount of physical activity appropriate to the situation (where hyperactivity is also present, - may be limited to restlessness in adults).

Many people may experience these symptoms sometimes, but for someone with AD/HD they are pervasive and debilitating (in some cases to the point of making day-to-day functioning extremely difficult).

Occasioanlly, under certain circumstances, people with AD/HD can 'hyper-focus' for a period. Usually during high intensity, interesting or stimulating situations that provide rapid results (in front of the TV or Playstation is a common example). This inconsistency has lead some people to question the strict use of the term 'deficit'.