Does "подруга" mean girlfriend as in "girl friend", ie a female friend, or as in "girlfriend", a romantic interest?
Doing a google image search for подруга seems to be getting matches for both types.
"Girlfriend" and "boyfriend" are most usually conveyed in Russian as девушка and парень (or молодой человек).
Подруга usually means "girlfriend" as well but its meaning is somewhat less suggestive of a romantic relationship than that of девушка.
As a male you do not call your female friend подруга, not without raising an eyebrow. Women, on the other hand, could refer their female friends as моя подруга (while using моя девушка would unequivocally imply romantic relationship with her).
If you want to rule out any romantic component in describing your friendship, you should use знакомая ("acquaintance") or приятельница (female equivalent of "buddy").
In addition to other answers (especially Quassnoi's)
From time to time old-fashioned peoples (like grand parents) can use 'подруга' in meaning "girlfriend":
Also when you talking about specific women, you can use "подруга" in meaning GF:
Between man and woman "подруга" can means "GF" or "friend".
Between woman and woman "подруга" will be always means "friend".
"Подруга" it's an undefined state. If you'd way
Usually people would ask you:
Cause your relationship isn't clear for them.
Она мой друг. Мы друзья. (She is my friend. We are friends)
When the girl uses this word for another girl, it always means a female friend. Used by man, it could have one of two values. Sometimes it's something between. But it definitely describes not-so-romantic relationships.
Can be any meaning depending upon context: one can use it when talking to others about his girlfriend.
When used by males has a connotation of long term relationship or a connotation of age of the couple (say 30+).