"can someone define "Fine Art Photography" for me please?"

Nah, that would spoil all the fun. Just think about all the empty lives if everything had agreed definitions.

Indicators might be--

Fine art costs more than the buyer thinks its going to

Its fine art when its sold through an expensive gallery, with multiple mark-ups.

Its fine art when the seller or photographer think its good.

Its fine art when its only functionality is to cover that stain on the wallpaper.