well, i can see the first two responders are fountains of knowledge.
Artificial Intelligence. Meaning it is a machine with enough sophistication to display sentience. You think computer, you think of your Dell. I say AI, i mean every computer in the world right now several times over combined into a box the size of your head. Computers are constantly getting faster. once they are fast enough, and complex enough, they will mimic the way the brain works. Think realy hard, about your mind. Your mind is neurons and such, all a comptuer has to do is simulate that soo well, that it stops being a machine and starts being alive....