ADD is:
a disorder of the nervous system characterized by disturbances in the areas of attention, impulsiveness and hyperactivity.

(I'm
not sure
I like
the use
of the term
'disorder'
myself)
ADD is a complicated syndrome with diverse symptoms of varying degree.  Anyone can sometimes have lapses in memory, act impulsively, or have difficulty concentrating.   The problem with ADD is one of degree and persistence of the symptoms over time and across varying situations.

        ADDers have symptoms that begin in childhood and cause significant problems in school, work and relationships.

(might
just
be
a
gift)

(or an evolutionary trend)
from "You Mean I'm not Lazy, Stupid or Crazy" by K. Kelly & P. Ramundo

ADD Diagnostic                                           
What to do about it