Language input refers to the exposure a learner has to spoken or written language. It includes any form of communication that provides examples of how a language is used, such as conversations, books, movies, and songs. This input is crucial for language acquisition, as it helps learners understand vocabulary, grammar, and pronunciation. Effective language input should be comprehensible, meaning it should be slightly above the learner's current level of understanding. This concept is often associated with Stephen Krashen, a linguist who emphasized the importance of meaningful exposure to language for developing proficiency.