The term "interlanguage" comes from Larry Selinker who, in 1972, defined it as "a separate linguistic
system based on observable output which results from a learner's attempted production of a target language
The American Heritage Dictionary of the English Language, Fourth Edition gives two definitions:
1. The type of language produced by nonnative speakers in the process of learning a second language or foreign language
2. A lingua franca
Interlanguage lives in the space between languages.