Wiktionary
cdo-squared
n. (context finance English) A type of CDO (collateralized debt obligation) that invests in other CDOs.
Wikipedia
CDO-Squared
CDO-Squared is a collateralized debt obligations backed primarily by the tranches issued by other CDOs. These instruments became popular before the financial crisis of 2007–08. There were 36 CDO-Squared deals made in 2005, 48 in 2006 and 41 in 2007. Merrill Lynch was a big producer, creating and selling 11 of them.