A girl with a very sexy body but an unattractive face... This phrase is generally uttered by men who examine the posterior of a lady as they drive by, On the approach they say "Oooohhh" and if her face does not match the beauty of her posterior as they pass they will say "Naaaaaa", hence Una.
Very good (contrary to the dictionary definitions of "full of or involving woe" and "lamentably bad or serious"). Also used as an adverb before adjectives (but not as "woefully") to mean "very".