What does it mean to be sentenced to two consecutive life sentences?

Each person only has one life they can spend and I doubt the sentences get passed on to their kids :-P lol. So whats the point of having two consecutive life sentences?

By the way, I read that on the second line of the "plot" section of this page: http://en.wikipedia.org/wiki/The_Shawsha...
Update: The answers haven't explained anything up to now... I KNOW that it means the person won't get out of jail but isn't that what a life sentence is already? So do you need more than ONE LIFE sentence?
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