Everyone has different ideas of what it means to be fluent, of what requirements must be satisfied before you can say, Im fluent in Tibetan, or whatever. There is no universal definition or accepted standard of fluency. I tend to have the same definiton as ｔhe first two posts, tiulpan and LGF92. If your speech flows naturally, if you can spontaneously form long and informative sentences, using appropriate tenses, conjugations and turns of phrase, and without pausing to search for the right word, without using the wrong word or words that sound the same ( a much bigger problem for learners of tonal languages like mandarin, khmer etc, but equally challenging for learners of non-tonal languages like Japanese, I still sometimes confuse 広告koukoku , and　報告 houkoku) 　and without having the listener ask you to repeat what you said or clarify what you mean, when talking about ANY topic that you can discuss in your maternal language, then it could be said that you speak fluently. A lot of language learners get fixated on the notion of 'fluency' and are often premature in claiming that they have attained it. They may be good at using the vocab and sentence patterns they have learnt, they may well be able to use them at natural speed, thereby giving the impression that they speak the 'entire language' fluently, but, once the topic of conversation wanders into areas that they have never discussed, it soon becomes obvious that they still have a lot to learn. Although its fun and interesting to know where you are on the fluency meter, it can be a trap too, for those who think they are already fluent when they are far from it. They get a false sense of completion and lose the drive to power on and approach native proficiency. Aiming to speak well, and continually increase your content versatility is, it could be argued, a better mindset to adopt.

I think your thought has been thought by many language learners. We all expect someday we speak foreign language fluently..When I started to learn English, I hoped that after learning hard a certain period of time and one day morning when I wake up I found myself could speak English fluently like native. But on the next second, I thought my thought was such ridiculous just like a magic change. We all know this change is gradual as the change between seasons.But on the other hand, we suppose that there must be a line between "I can speak fluently" and "I can't speak fluently" certainly(the point is can or can't) because "can" can't equal to "can't". In this suppose, the change seems as "snap" result.. Does it seem incompatible with "gradual" as the common sense on learning and "snap" as the switch from can to can't? I don't think so. I think the process of learning a foreign language is of course gradual and the switch from "I can't speak a foreign language" to "I can speak a foreign language" is a snap change result, and this switch happens after we have learned the last word in the language or say, there would be no word we don't know in the language we learn.But unfortunatly, the seperate line or switch we thought it must be exist would never happen because no one could know every thing or word about a language. Just as you say you even don't know every word in English as a native. So, I think we may change our thought on learning foreigh language. life or sociaty has many sections,but each people is single one. Our environment including people, work and so on we could see or touch is only a small part among those sections. So we could try to speak about the things nearest aroud ourselves at first in foreign language fuently. Just as Eliot say "on the "DAILY basis".As we are in touch with things a little more and more, we could accumulate foreigh words a few more and more. And it is easy to fluent a word,just repeat it 3 times. To say extremely, Suppose if you have a Chinese neiborhood,and first day you met him when you are running on morning,you just need say "Hello". so Chinese word "你好 ni hao" you speak fluently in totally enough to you.And next day, he wake up and runing with you. You both keep running and chating,say hello and then about whether."Hello!It is a nice whether" in Chinese is "你好，今天天气不错 ni hao, jin tian tian qi bu cuo".And day after day, as you talk more and more, you could speak more Chinese fluently day by day. From simple to complex, fanilly you could speak fluently in foreign language you need. Your friend Eliot say "DAILY basis", I wanna add one,it is "NECESSARY basis".No one could make a huge progress in one day.we are all walking to success in a long way.But it is easy to keep progress a little more,and the points are where and how we should put our limited energy in. Here my answer is that the "where" section that is necessary to us and the "how" is to keep fluent on the "where" section.

I find that after a while you can teach your brain to switch into thought in a certain language - this happened in my 6th year of French when I could sit, watch a film and about 90 minutes in my head would understand everything a lot better, and sometimes I would finish watching it and find it hard to flick back into English! Over time this duration gets shorter and shorter and eventually, I think when you have that down to a few minutes (I can do it in about 10 minutes at the moment in French) then you can consider yourself fluent. It is very gradual though, don't expect anything just to hit you in the face one morning. I didn't realise it until I started oral classes at university.

Well, yes, you wake up one day, go about your business, and suddenly the lingo is flowing in a way like never before. you cannot predict that point. From experience, it took me 3-4 months of studying German amongst German speakers on a DAILY basis. The important word here is DAILY. A couple of hours a day should do it. You'll get there.

Yes, you are right, the speaking fluent means that you speak, for example, in English or Japanese/Chinese without thinking is your current speach Ok according to the basic grammar of this language which you speak just now. That is a main thing!