In 1979 Cummins coined the acronyms BICS and CALP to refer to processes that help a teacher to qualify a student's language ability.
BICS refers to the basic communicative fluency achieved by all normal native speakers of a language.
It is cognitively undemanding and contextual and is better understood as the language used by students in informal settings, say, on a playground or cafe.
Research by Cummins as well as Virginia Collier suggest that it typically takes language learners 1–3 years to develop BICS if they have sufficient exposure to the second language, "with the exception of severely retarded and autistic children".
[1] CALP refers to the ability to manipulate language using abstractions in a sophisticated manner.