I've tried many combinations that i think they should accepted, and reported them: i.e: "my girlfriend was waiting outside for one hour" (it could be 2, 3,... And the expression Девушка itselves can be translated as "my girlfriend" by "sensum"), or "the girlfriend was waiting outside for an hour" (to be more correct gramatically), and others, but the only accepted form is "the girl waited outside for an hour"
If they wanted to say "my girlfriend" it would've been "моя девушка". The word "девушка" doesn't have an inherent meaning of "girlfriend", and on it's own ot only means "girl". Or "young woman" to be precise.
Using the posessive is essential for the words "девушка" and "парень" to mean "girlfriend" and "boyfriend" respectively, and this meaning is very recent. Imagine if in English they started using expressions like "my girl" and "my guy" when they want to say "the girl/guy i'm dating". This fact wouldn't change the fact that on it's own the words "girl" and "guy " don't have any relation to dating/
Yes, thanks for the explanation. I read (don't remember exactly if was a comment too) that in colloquial manner it's possible to refer to my girlfriend (father/mother/people/parents...) as only девушка (отца, мама,...), as in English or another languages ("(the) Girlfriend went to...", "La novia fue a...") and so. Anyway, the main thing is that only was accepted one right form, rejecting others that doesn't change the meaning of the sentence (like "the girl was waiting for one hour in the street")