Overcollateralization 

A type of credit enhancement in which the principal amount of collateral used to secure a given transaction exceeds the principal of the securities issued.

Remarks: Bond funds including mutual funds (open-end and closed-end, actively managed and indexed), exchange-traded funds and unit investment trusts offer a convenient and affordable way to invest in a diversified portfolio of bonds, but a bond fund investment can differ from a bond investment in ways that are important to understand.