Would love to have both providers and enthusiast's interpretation ... TIA

I'm thinking it means Fully-Functional.

Thanks - I knew the words, but what do they mean .... for example:  able to have a visible orgasm, or able to become erect ( the later does not imply the former ), or ....

Both, able to get hard as a rock and cum!

unless we are not talking about " FF" as 'Fantastic Four " (sorry,couldn't resist) when i see that term in an escort ad, i strongly assume "getting hard and staying hard". and just because the cock grows doesn't mean it will reach maximum erection (stiffness).. not enough to be able to penetrate or stay hard thru anal intercourse. Orgasm has nothing to do with the meaning of 'FF".

Don't ask me how I know !

Fully functional but does not necessarily ejaculate. Gets hard but may not pop.