Let’s discuss reactivity

So for starters, I’m curious what EXACTLY defines reactivity. When googled it states that, “reactivity is an intense, emotional response often times shown through lunging, barking or growling. These reactions are often due to fear, anxiety or frustration. Reactivity is separate from aggression as aggression is an intent to cause harm.”

Let’s also keep in mind that that the definition of “lunging” is typically used within the context of attacking. So with keeping that in mind it wouldn’t appear that reactivity (lunging, barking and growling) really separates itself from aggression in any meaningful way.

Now let’s relate this to puppies.. would a puppy on a walk that gets excited when it sees other dogs or people be considered reactivity? To me a puppy getting excited by dogs and people just seems like it is something that would inherently be part of a puppies playful, loving and curious nature. Would most of you consider a puppy wanting to pull, getting excited or struggling to focus because of playful excitement to be reactivity or would you not?

Lastly, if you do consider a puppies excitement to be a form of reactivity what are the best ways to start addressing it. If you do NOT view it as a form of reactivity do you believe that it is simply common for puppies to display these excitements and that they will naturally grow out of them?