In its initial form, interlanguage refers to the state a language learner finds themselves in when using a mixed form of L1 and L2 before being proficient in L2. This means the language learner may borrow rules and forms from their first language and apply them to their L2 output. This gives an incorrect output or “Interlanguage”. The same is true of new rules learnt for L2 which may be overused in situations where they do not apply.