What does the term "Random Keyed" mean when referring to door knobs?

I'm looking into buying a new door knob but i have no idea what "Random Keyed" means when i see it in some of these descriptions. Can anyone tell me what this means?
Update: This is the door knob i'm looking into buying...
http://www.amazon.com/gp/product/B008BYQAX8/ref=ox_sc_act_title_2?ie=UTF8&psc=1&smid=A2RFSIF56F6W5J
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