What is a "Toxic Asset?" Please explain. Does congress understand?

When they talk of toxic assets in the media they mean loans which have little chance of being paid and likely will be foreclosed. Even though the property is worth something at foreclosure, it often costs more than its worth to foreclose (legal and other expenses), repair (many owners trash their home before they give it back to the lender) and then maintenance and selling expenses until it can be sold. These loans held by banks and other institutions can drag the lender into bankruptcy when there are thousands or millions held by one institution.