Fossilization and interlanguage are examples of language teaching jargon. These kinds of technical terms that are associated with language teaching often strike me as unnecessary, and not helpful to language learners. I know that learners are not aware of these terms. However they are often used by experts in Second Language Acquisition, and people who teach teachers how to teach languages. I feel that these terms have had little if any positive influence on language learning. Language learning still comes down to motivation, time on task and the ability to notice. Here is a recent youtube video I did on the subject.