According to the text, the concept “additional language” refers to

Content and Language Integrated Learning (CLIL) is a dual-focused educational approach in which an additional language* is used for the learning and teaching of both content and language. That is, in the teaching and learning process, there is a focus not only on content, and not only on language. Each is interwoven, even if the emphasis is greater on one or the other at a given time. CLIL is not a new form of language education. It is not a new form of subject education. It is an innovative fusion of both. CLIL is closely related to and shares some elements of a range of educational practices. Some of these practices – such as bilingual education and immersion – have been in operation for decades in specific countries and contexts; others, such as content-based language teaching or English as an Additional Language (EAL), may share some basic theories and practice but are not synonymous with CLIL, since there are some fundamental differences. CLIL is content-driven, and this is where it both extends the experience of learning a language, and where it becomes different to existing language-teaching approaches.

* “often a learner’s ‘foreign language’, but it may also be a second language or some form of heritage or community language.”

(COYLE, Do; HOOD, Philip; MARSH, David. 2010, p. 1. Adaptado)