This was mostly a thing in the PS1 and PS2 eras. The first genre was the point and click PC adventure game, ie the thing we still think of when we hear the words “adventure game” to this day. The second definition was much less well defined and encompassed games like Tomb Raider, Shadow of the Colossus, the Ubisoft Prince of Persia games and Soul Reaver.
I think it was just used as a catch-all term for any kind of console third person 3D action game with platforming elements that couldn’t be easily classed into other genres
“Platformers don’t exist outside of niche steam games”, said Elephant Mario as he slowly faded into nothingness, while a stream of tears ran down his face. A moment later the trombones finally stopped playing. He was gone.