collateralized mortgage obligations是什么意思?

collateralized mortgage obligations是什么意思? collateralized mortgage obligation是什么意思?如题. 英语翻译they were underwater,meaning with a mortgage larger than the value of the house.怎么翻译?There are over 80 million single family homes in America,and it's estimated that in 2011,18 million of these were underwater,meaning with a mortg