Chunking
Chunking is grouping small pieces of information together so your brain can remember more at once.
Think of it this way
A kitchen tray holds many small items. You can group them into sections: spices in one corner, jars in another, and cans in the last. Your brain treats each group as one item, not five or ten. This is how chunking lets you hold more in mind at once.
Explaining chunking by grade level
Think about a long phone number. It is hard to remember all those digits. Now break it into small groups of three or four. Your brain holds each group as one piece, so you remember more.