What is the floor of a fireplace better known as?

My job was to empty the ashes in the mornings, before laying a new fire with kindling I had just chopped and then bigger pieces of wood I had stacked the wood boxes full of. I loved cooking with toasted sandwich irons. We had one that made 3 in one go!

I had no idea! But now I know the bottom of a fire place is a hearth! Hmm that’s cool!

And the best place by the fire was always reserved for the storyteller.

I've also heard of a hearthstone - presumably from the days when the fire was just built up on a stone, definition given by OED is " a flat stone that forms the hearth or part of a hearth" . So, stone could also be a correct answer.