Money which is an asset to those who hold it, but is not a liability for anybody else in the economy. This is the case for gold coinage, but not for bank balances. Outside money is contrasted with inside money, where the asset for the holder is balanced by a liability of the bank issuing the money. It is a matter of definition whether money which is a government liability is outside or inside money.
|Reference: Oxford Press Dictonary of Economics, 5th edt.|