第二語言
"Second language" refers to any language learned in addition to a person's first language; although the concept is named "second"-language acquisition, it can also incorporate the learning of third, fourth, or subsequent languages. Second-language acquisition refers to what learners do; it does not refer to practices in language teaching, although teaching can affect acquisition. The term "acquisition" was originally used to emphasize the non-conscious nature of the learning process, but in recent years "learning" and "acquisition" have become largely synonymous.