Comment by corysama
It is a bit of a silly term. It was made mostly to contrast against the somewhat more adhoc methods that preceded it. The new technique was parameterized more around physical properties where the older ones were more about visual descriptions.
This paper from Disney is what kicked off the movement https://disneyanimation.com/publications/physically-based-sh...
What’s hilarious is there’s nothing physically based about the Disney model. It’s empirical and It’s not even energy conserving.
As sibling pointed out, physically based rendering precedes “PBR” by a looong time and goes much, much deeper than “I put a metalness map in my shader”