what is the united states net interest spending and who receives this?

I was reading the citizens guide to 2010 financial report of the united states government chart two depicted a forecast of the net interest spending of the united states government to be increasing every year through 2085 while non interest net spending is to stay the same. What exactly is this "net interest spending"?
http://www.fms.treas.gov/frsummary/frsummary2010.pdf
 
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