Interlanguage is the term for a dynamic linguistic system that has been developed by a learner of a second language (or L2) who has not become fully proficient yet but is approximating the target language: preserving some features of their first language (or L1), or overgeneralizing target language rules in speaking or writing the target language and creating innovations. An interlanguage is idiosyncratically based on the learners' experiences with the L2.