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.