Are all prop logic wffs sentences? Why aren't there any free variables?

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In propositional logic is it correct to say that all wffs are also sentences/statements? Are sentences and statements the same thing?

I also read that sentences are wffs that lack free variables, but this seems more like a first order logic concept. Does this still apply to propositional logic? If so why are all variables considered bound? Just because they're all either true or false and nothing else?