Fluency means you can communicate in the total amount of situations that you need to be able to communicate in.
I think of the total number of possible situations in life as the denominator of a fraction, and the number of situations in which you can communicate as the numerator.
For example, let's say that in your entire life there are 10,000 different kinds of situations, and as a fluent speaker (according to my definition) you can express yourself easily in all 10,000 situations. Then your fluency level is 10,000/10,000, or 1/1.
Or let's say you live a simpler life and only 100 different kinds of situations ever arise. As a fluent speaker you would be 100/100, or also 1/1.
As a side note, you don't actually have to experience anywhere close to 10,000 situations to be able to achieve 1/1 fluency. In fact, the actual number of situations you need to experience is much less than 10,000 because the same grammatical patterns and vocabulary simply recur, with variations.
When people begin learning a new language, they imagine that the total amount of situations in which they'll have to communicate is infinite. So when they learn to communicate in one situation, their fluency level is 1/∞. When they can speak in two situations their level is 2/∞. And when they can speak in 100 situations their level is 100/∞. That outlook is frustrating, because you're always inifinitely far from fluent.
My view is that if there is only one kind of situation that ever comes up and you can communicate in that situation, then you are 1/1 and fluent. For example, if all I ever have to say in a foreign language is 'ticket please, thank you, ticket please, thank you', then as soon as I can say 'ticket please, thank' I am fluent in the language.
Of course most people have more than one total situation in which to communicate, but it's not as many as you'd think. Add to that the idea that the grammar and lexicon of a language is finite (and smaller than you might expect) and it's simply a matter of mixing and matching words of phrases you've learned from previous situations, and it's not hard to reach 100/100; or 10,000/10,000; or 1/1.
If it seems disingenuous to say that someone who can speak in only one situation is fluent in the language, just keep in mind that even though I can speak in 10,000 of 10,000 situations in my native language, there are still many situations in which I can't speak -- such as calculus, economics, needlepoint, and so on. It's just that no one knows what I don't know because I'm never in those situations, and I can maintain my fluent status.
To conclude, if you let what you truly need to say drive what you learn, you can achieve a good level of fluency in a language even as a beginner. A week of practice might look something like this: 0/1, 1/1, 1/3, 3/4, 5/8, 10/13, 20/21.
The alternative is to imagine all possibilities as infinite, and forever be at 0.