Umbrella insurance
It's basically a liability insurance.
Suppose somebody got hurt either in a car accident, or some accident in your house, your auto or home insurance would kick in after you pay your deductible. But in case you have other assets, the victim might want that too. So, they hire a lawyer and sue you for negligence. That's when umbrella insurance kicks in. It basically covers liability on top of auto/home insurance.
Generally, if you have any income-producing business or asset (such as rentals with meaningful equity), it's imperative to have umbrella insurance. Besides, it doesn't cost a leg or arm, so, why not.
See info from moneywatch.com and wikipedia:
http://moneycentral.msn.com/content/Insurance/Insureyourhome/P35349.asp
http://en.wikipedia.org/wiki/Umbrella_insurance
Hope this helps.
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