Fregna is a synonym of the word Fica or Figa, and it literally means vagina.
We usually use it to refer to a very beautiful woman, it exists also the word Fregno, which is used for handsome men.
It's largely used in central part of Italy.
Synonym for fica, fregna is the most vulgar Italian term to indicate a vagina, and indeed rather similar to the English word cunt.
It is often used together with the adjective "dry", as in "dry cunt", in Italian: "fregna secca".
The reference is mostly metaphorical in this expression, so usually not to a non-lubricated vagina, but rather more to a woman who is boring, rigid, uninspiring, no fun, skinny and wrinkly.