What term describes the application of grammar rules in instances where they do not apply, such as using "sleeped" instead of "slept"?

The term that describes the application of grammar rules in instances where they do not apply is indeed grammar overgeneralization. This phenomenon occurs when individuals, often children learning language, apply regular grammatical rules to irregular verbs or constructs. For example, using "sleeped" instead of "slept" reflects the overgeneralization of the regular past tense rule that typically adds "-ed" to a verb.

This concept is significant in language development, as it showcases how learners systematically acquire language rules and sometimes make errors by applying these rules too broadly. Observing this process helps linguists and psychologists understand the stages of language acquisition and the cognitive processes involved in learning to speak and write correctly.