It normally means. Hi gorgeous woman or Hello gorgeous man. The noun is dropped.

If someone were to say "Hey gorgeous" to someone else it would likely be a greeting or a pick-up line. A husband might use this line if he encounters his wife or if she walks in a room. It could also be used if a man or woman was trying to get someone of the opposite sex's attention.

thank you Donna, that's a really clear explanation = ) now I know why ~ the question have been stuck in my head for a while..

Hi Eric, Gorgeous is an adjective, but in this case it refers to a person and most probably girl/woman. The noun (that would have followed the adjective) has been dropped intentionally. It is an informal way talking to known acquaintances and there is nothing wrong with it. Similar examples would 'Hey beautiful' 'Hello handsome'