That is the total murders per the whole population, I believe. A rate of 8,583 per 100,000 would put as at something like 26 million murders in 2011. We love guns and murder, but not quite that much.
hmm, looking at the stats again, something doesn't seem quite right.
the 8,583 was just the absolute total, and not the rate per 100,000.
the fire-arms murder rate was 2.75 per 100,000, or in other words, 0.00275%.
now it's ok to for us to love guns and murder again!
edit: to put that murder number in perspective, i looked up the number of deaths per year from heart disease. apparently it's around 600,000 per year in america.