A second language is a language other than ones first language that is learned for utilitarian reasons because of its direct value to the speaker as a citizen of his own country. Second-language acquisition (SLA), second-language learning, or L2 (language 2) acquisition, is the process by which people learn a second language. When it comes to learning a second language (L2), learners build a system that is different both from that of the first language (L1) and the second language (L2).Even if it is idiosyncratic and constantly changing, it is nonetheless systematic. Learners do not willfully distort the native system but invent a system of their own.The term that has been given to this structurally intermediate status of the learners language system is interlanguage, by Larry Selinker (1972). This is also called transitional competence or approximate system.'Interlanguage' in second language learning refers to the language system which each learner constructs at any given point of development and it also refers to the range of interlocking systems that characterizes the development of learners over time.Thus, interlanguage is like a third language system. It is dynamic, always growing, and always is in a state of flux. It is systematic, it has order €“ that is, it is structured like all languages. It is always open and ready to receive more input.Hence, it is clear that 'Interlanguage' in second language learning refers to the language system which each learner constructs at any given point of development.