ADHD (Attention Deficit Hyperactivity Disorder) is a psychiatric disorder in children. As the name suggests, children with this syndrome cannot pay enough attention to anything, and are usually overly active in everyday matters.
You should always know that ADHD is not always about affecting children. Some adults also suffer from this disorder. Studies show that about 4% of adults in the US also have ADHD. It is most likely that they developed it in childhood and may not be diagnosed until later in life.