What is the difference between ADHD and ADD (Attention-Deficit Disorder)?

What is the difference between ADHD and ADD (Attention-Deficit Disorder)?

ADHD is the only term assigned to this diagnosis but there are different presentations of ADHD — ADHD Inattentive Presentation, ADHD Hyperactive/Impulsive Presentation, ADHD Combined Presentation (both inattention and H/I behavior) and a fourth type called Unspecified ADHD, a diagnosis used when symptoms are unclear.