Errors are a natural part of language learning and occur when learners attempt to produce language structures beyond their current abilities. There are several types of errors, including those due to interference from the learner's first language, developmental errors from overgeneralizing rules, and slips from lack of concentration. Learners' developing language system is called an "interlanguage" which is not fixed but progresses as they incorporate corrections and new structures. While errors indicate areas for improvement, teachers must determine when and how to provide feedback, as immediate correction may not be helpful and allowing mistakes in fluency activities can build confidence.