ADHD, or attention-deficit/hyperactivity disorder, is the only clinically diagnosed term for disorders characterized by inattention, hyperactivity, and impulsivity used in the American Psychiatric Association’s Diagnostic and Statistical Manual of Mental Disorder, Fourth Edition.
There are actually three different types of ADHD, each with different symptoms: predominantly inattentive, predominantly hyperactive/impulsive, and combined.
This is not a sign of stupidity; in fact, ADD frequently affects those with above average IQ's, such as Ivy League students, and many renowned geniuses throughout history. Though the occasional genuine moron and/or average thinker will fall victim.
A test of whether or not the condition is actual could be if the individual in question has difficulty focusing on the activities they enjoy as well as activities they dislike.