The language we use for day-to-day, face-to-face interaction is known as :

Linguist Jim Cummins distinguished two dimensions of second-language proficiency: Basic Interpersonal Communication Skills (BICS), the everyday, context-embedded conversational language used in face-to-face social interaction, acquired within about one to two years; and Cognitive Academic Language Proficiency (CALP), the abstract, context-reduced academic language needed for schoolwork, which takes about five to seven years to develop.

The stem asks for the term describing language used for day-to-day, face-to-face interaction. This is exactly Cummins' definition of the everyday conversational register.

Contrasting the offered terms:

• CALP names the opposite construct: abstract, academic, textbook/classroom language, not casual conversation.

• "Communicative language skills" is a generic descriptive phrase; it does not name Cummins' specific two-tier framework.

• "Interpersonal language proficiency" sounds similar but is not the established coined term; the actual coined term is Basic Interpersonal Communication Skills.

So the language used for day-to-day, face-to-face interaction is known as Basic Interpersonal Communication Skills (BICS).