(i was just discussing this over at how-to-learn-any-language.com and i figured i should post it here too)
I don’t think there’s much point in universally defining the term “fluent”, but for me it holds a useful purpose as a goal in my learning. I view “fluency” as that point where I can use the language without thinking about it consciously, and have a good conversation with someone about any topic that doesn’t require special education. Also, my accent should be good enough that I don’t have to repeat my words in order for native speakers to understand them.
When I try to apply these standards to some of the people I know, I think it fits quite well with my opinion of “who needs to study more” vs. “who is good enough”. For instance, I have two coworkers who are clearly not native speakers of English, but I would classify them as “fluent” as defined above. I never have to ask them to repeat their words, and they talk naturally without stopping, so it seems like they do it effortlessly. Sure, they make mistakes, and they don’t have a perfect accent, and there are some special topics that cause difficulties, but I can still easily classify their English as “good enough” in my eyes.
I have two other coworkers, however, who have trouble getting understood. They can talk about a lot of topics, sure, but people often have to ask them to say some words multiple times because they just can’t understand what word it was. Also, their grammar is noticeably weird, so I sometimes have to think about it a bit in order to get their meaning. For these two people, I would not call them “fluent” as I defined it, because I (as a native speaker) have to put in so much extra effort in order to get what they’re saying, and because it seems difficult for them to formulate things in the language.
Although they still manage to communicate quite well about many things, I would classify their skills as “needs more work”, and therefore as not yet fluent. In this sense, I see “fluency” as a worthwhile goal for myself. I want people to be able to understand everything I say without them putting in a lot of extra effort to figure out what I said. I want to effortlessly speak the language, and I want other people to effortlessly understand what I just said. Maybe I won’t be perfect in all ways, and maybe I won’t understand all sorts of obscure cultural references that they say, but all the stuff that I say will be clear, fluid, and easy to understand.
Becoming fluent is still a challenging and useful thing with this definition, but is clearly far below the level of a native speaker (linguistically and culturally). Right now, I understand almost everything I read in German, but my speaking ability would not pass this test, so I wouldn’t call myself “fluent”