What is the homunculus?

From the text:

Because people can see the screen inside their head and they think there is someone in their head sitting there looking at the screen, like Captain Jean-Luc Picard in Star Trek: The Next Generation sitting in his captain’s seat looking at a big screen. And they think that this person is their special human mind, which is called a homunculus, which means a little man. And they think that computers don’t have this homunculus. But this homunculus is just another picture on the screen in their heads. And when the homunculus is on the screen in their heads (because the person is thinking about the homunculus) there is another bit of the brain watching the screen. And when the person thinks about this part of the brain (the bit that is watching the homunculus on the screen) they put this bit of the brain on the screen and there is another bit of the brain watching the screen. But the brain doesn’t see this happen because it is like the eye flicking from one place to another and people are blind inside their heads when they do the changing from thinking about one thing to thinking about another.