When a person can speak a foreign language well, we often say that s/he speaks it fluently. Yet not many people, teachers included, know what exactly fluency is all about or can define it properly. Luckily, there is always a book out there where they tell you definitively what the concept of interest to you means and «fluency» is no exception in that respect.
According to J. A. van Ek and J. L. M Trim (Vantage, CUP, 2001, page 117)
Fluency, which term may be used for productive as well as receptive ability, involves:
- ease of access to and retrieval from memory;
- command of discourse strategies;
- rate of delivery and processing
As can be seen, fluency is not equal to speed, so when someone is able to speak very fast in a foreign language, it does not necessarily mean that the person is fluent. In addition to speaking fairly quickly, s/he also has to have an adequate command of the linguistic apparatus (grammar, vocabulary, etc) and a sufficiently well developed compensatory competence (i.e. adequacy in using repair strategies and avoidance strategies) so that s/he could continue the flow of communicative interaction in spite of gaps in his/her linguistic ability.