Inattention is one of the major symptoms of ADHD, although it is still greatly misunderstood. Some experts believe that it is "over" attention, rather than inattention. People with ADHD do not have the ability to filter out unwanted stimuli and therefore, they pay attention to everything, rather than being able to focus on one thing. Inattention is also described as being easily distracted.
For more information:
Inattention - ADD/ADHD Symptoms
ADHD - How Are ADHD Symptoms Manifested in Children?

Why Alcohol and Adderall Do Not Mix
What Causes ADHD: Myths vs. Facts
10 Medical Conditions That Share Symptoms With ADD/ADHD
10 Myths About ADHD