What phenomenon occurs when incorrect forms a learner of a second language has developed become permanently fixed due to lack of correction?

The correct answer is fossilization, which refers to the process where incorrect language forms that a second language learner has developed become ingrained and resist correction over time. When learners repeatedly use incorrect structures without receiving feedback or correction, these errors can become a stable part of their language use. This phenomenon can occur in the context of grammar, pronunciation, or vocabulary.

Fossilization can hinder a learner's progress in achieving fluency or native-like proficiency because they may not recognize their errors as mistakes that can be improved upon. Understanding fossilization is crucial for educators and learners alike, as it highlights the importance of regular feedback and correction in the language learning process.

The other options relate to different linguistic concepts. Language interference involves the influence of a learner's first language on their second language use, which is not specifically about the entrenchment of errors. Dialect variation refers to the differences in speech patterns within a language based on region, social class, or other factors and does not pertain to the individual errors of a language learner. Overgeneralization is when learners apply a grammatical rule too broadly, leading to errors, but it does not capture the aspect of errors becoming permanent fixtures in a learner's language use.