Comprehensible input is language input that can be understood by listeners despite them not understanding all the words and structures in it. It is described as one level above that of the learners if it can only just be understood.

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What Is Comprehensible Input?

Comprehensible input is language materials that you can experience and understand nearly all of the content presented. In short, it is language learning material in your target language slightly above your abilities. That way, you understand most (but not all) of it. In other words, it’s the Goldilocks Zone of language learning. Not too hard, not too easy.

(https://www.optilingo.com/blog/language-learning-essentials/comprehensible-input-how-you-learn-a-language/)

According to language learning research, you should
1. Read for pleasure
2. Read books that you understand 98% of (most students are reading books and articles that are too advanced)
3. Read extensively (read as much and as fast as possible, without slowing down to look up every word)
4. Read narrowly (read material by the same author or on the same topic)

Source: italki

Comprehensible input