The nature of learner language

Second Language Acquisition by Rod Ellis (1997)

New Words
Overgeneralization: the oversuppliance of an interlanguage feature in contexts in which it does not occur in target-language use (e.g. ‘He ated ice-cream.’) Overgeneralization result in errors.
U-shaped course of development: The pattern of learning evident when learners use a correct target-language form at one stage, replace it with an ungrammatical interlanguage form, and then finally return to use of the correct target-language form.
Restricting: The process by which learners reorganize their interlanguage in the light of new evidence about the target language. It can occur as a result of a shift from item learning to system learning.
Form-function mappings: The identification by the learner of a particular function which can be performed by means of a particular form. The ensuing ‘mapping’ may or may not correspond to target-language norms.
Free variation: The random use of two or more variants of a structure.Fossilizatioln: the process responsible for the cessation of learning some way short of target-language competence. Most L2 learners’ interlanguages fossilize