There’s a lot of confusion around which terms to use when discussing attention deficit hyperactivity disorder. Is ADHD the same as ADD? Should they be treated differently?

Let's clear things up
First of all, ADD and ADHD are actually referring to the same thing. “ADD” stands for attention deficit disorder which was its previous name before it was changed to “ADHD” in 1987. That definition was revised in the 1990s to include three subtypes of ADHD: predominantly inattentive ADHD, hyperactive-impulsive ADHD, and combined ADHD. Confusing as that sounds, it’s actually still an upgrade on what was used in 1968: “Hyperkinetic Reaction of Childhood”.
Nowadays, when people say “ADD” they are usually referring to the inattentive type of ADHD. However, clinical use of this term has been almost entirely phased out - it’s all ADHD these days.
So, how is "ADD" different from ADHD?
“ADD”, or predominantly inattentive ADHD, typically causes problems with organization and concentration. This type is not always as obvious as hyperactive ADHD, and symptoms usually appear in a person’s work or school life. Someone with inattentive ADHD may have trouble keeping their focus on their work, becoming easily distracted and often making careless mistakes. Other symptoms include:
Struggles with following instructions
Fails to complete tasks at school/work
Seems like they’re not listening when spoken to
Has trouble with organization
Often hesitant to complete tasks that demand a great amount of mental effort
Loses things often (particularly necessary items for school/work)
Forgets things frequently
Alternatively, the predominantly hyperactive-impulsive type of ADHD is typically easier to spot. It is characterized by restlessness, high energy levels, and impulsivity. A person with this type of ADHD may show some or all of the following symptoms:
Frequent fidgeting or squirming, particularly when seated
Can’t seem to remain seated when required
Frequent running or climbing during inappropriate times
Seems to be unable to take part in recreational activities quietly
Is often “on the go”
Excessive talking
Blurts out answers to questions before the speaker is complete
Has difficulty with patience or waiting their turn
Frequently interrupts/intrudes on others conversations or activities
Some people with ADHD find that their symptoms reflect a mix from both the inattentive and hyperactive-impulsive types - leading to a diagnosis of combing ADHD. This is the most common presentation of ADHD.
While ADHD has these distinct subtypes or “presentations”, those diagnosed can show any number or combination of these symptoms throughout their lifetime. As for the terminology, ADHD is the official name - but depending on your diagnosis, maybe you feel “ADD” suits you better.