Attention deficit disorder (ADD) is an old term for primarily inattentive ADHD (attention deficit hyperactivity disorder). ADHD is a developmental disorder characterized by symptoms of inattention (such as distractibility, disorganization, or forgetfulness) or by symptoms of hyperactivity and impulsivity (such as fidgeting, speaking out of turn, or restlessness). It is also referred to as attention deficit-hyperactivity disorder (ADHD). ADHD is not caused by an underlying physical or mental disorder.
Jameson, J. Larry, et al. Harrison's Principles of Internal Medicine, 20th Ed. New York: McGraw-Hill Education, 2018.