When a person can speak a foreign language well, order 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