The term Walk Off

[Gurds]

It seems like everything is a 'Walk Off' these days.

Explain to me like I'm 5 what it means.

Last night for the Cards/Dodgers game, bottom of the 9th. One on, two out, a 2-1 count. Chris Taylor hits a HR.

To me, that isn't a walk off. That's just winning the game.

To me, and I guess I'm wrong, but a walk off would be if the first batter hit a HR on the first pitch in the bottom of the 9th to end win the game.

So please what is a "walk off"

Thanks!