Support Tranche 

A CMO tranche that absorbs a higher level of the impact of collateral prepayment variability in order to stabilize the principal payment schedule for a PAC or TAC tranche in the same offering. Also known as a "companion tranche."

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.