This is based on observations of a listening period in infants when they learn a first language.
Example
When learners begin to study a new language, they can go through a silent period where they are exposed to sufficient comprehensible input to allow them to begin to acquire language.
In the classroom
Common classroom techniques can address the needs of learners in a silent period, e.g. listening comprehension and vocabulary input. There are also methodologies which explicitly incorporate a silent period, such as Total Physical Response and the Natural Approach.
Further links:
https://www.teachingenglish.org.uk/article/total-physical-response-tpr
https://www.teachingenglish.org.uk/article/extensive-reading-why-it-good-our-students%E2%80%A6-us