Fluency

Fluency is the property of a person or of a system which delivers information quickly and with expertise.

It implies very good information processing speed, i.e. very little average time between successively generated messages.

Fluency is also proficiency in a language, most typically foreign language or another learned language. In this sense, "fluency" actually encompasses a number of related but separable skills:

Reading: the ability to easily read and understand texts written in the language;
Writing: the ability to formulate written texts in the language;
Comprehension: the ability to follow and understand speech in the language;
Speaking: the ability to speak in the language and be understood by its speakers.

To some extent, these skills can be separately acquired. Generally, the later in life a learner approaches the study of a foreign language, the harder it is to acquire auditory comprehension and fluent speaking skills. Reading and writing a foreign language are skills that can more easily be acquired after the primary language acquisition period of youth is over, however.