Interlanguage

a learner's version of his or her target language at a particular point in development.

Language in process
Although interlanguage is not a complete language, it is still a rule-governed system. It is a language in process.

A learner's interlanguage includes all the vocabulary and grammar learned to that point. It is revised each time the student acquires new information about the target language.

See interlanguage development.

Bruntt, Karen and Bryanne, Ulla. Handbook for Grammar Detectives, page 22.