SIV. A type of fund which invests in long term, high-yield securities with money that it raises by selling short-term securities of lower yield. The difference represents the profit made for investors. A structured investment vehicle often invests in asset-backed securities or corporate debt. SIVs were introduced in the 1980s, but ceased being used in 2008 due to the subprime mortgage crisis. Although SIVs were not considered very risky, the funds were based on the performance of commercial paper, which lost virtually all liquidity due to the subprime crisis.