To add to this, central banks don't lend out cash without banks pawning an asset in return. And they only do so on a limited time basis. The banks have to promi

To add to this, central banks don't lend out cash without banks pawning an asset in return. And they only do so on a limited time basis. The banks have to promise to repurchase the pawned asset at a certain date, hence the name "repo" (reverse repo from the central bank's perspective). Central banks are basically pawn shops that get to create their own cash to lend out.