A language – mother tongue, the language the interpreter works into from all his/her other working languages
B language – a language the interpreter works into from one or more of his other languages, and, although not a mother tongue, a language of which the interpreter has perfect command; the interpreter also works from this language into his/her A language
C language – a passive language from which the interpreter works into his/her A or B language but into which he/she does not interpret