This refers to the knowledge a reader already has about the information being read which needs to be applied in order to make sense of this new information. The knowledge about the world which children possess is, it seems, fairly crucial to them reading effectively.

We have to know something to learn something. Readers filter everything through the knowledge they already have. Willingham 2006

More Resources:

Listen to Science of Reading: The Podcast - Season 2, Episode 7. Research, comprehension, and content-rich literacy instruction: Sonia Cabell to learn more about background knowledge.

Building Background Knowledge - Reading Rockets

Content borrowed from R.I.S.E Arkansas Dept. of Ed