It means you look at them. Whereas with the MC you experience the story (esp. personal issues) from within them, from their perspective.
However, it's important to note that these perspectives are best seen when you're considering the story at a higher level than the words on the page. e.g. the level of an outline or detailed synopsis. Or, if it's a novel you've read, when you're thinking about it a week after finishing, and have some distance from those IC POV scenes.
Now I think there probably is some structural advantage to not have the IC as a POV character in a novel. However, I think most of the advantage is for the Author. I think readers' story-sense can handle the IC in close perspective, seeing their thoughts and dreams etc. as long as at the higher synopsis level they are still the "you" perspective. But if you're the Author writing the IC POV scenes in really close perspective, and you're really getting into the IC's mind, you might end up making things too personal at that higher level (synopsis level). I'm really not sure how much of a problem this would be; there might even be a trade-off between structure and storytelling, between a more memorable story vs. making it more fun to read in the moment. I really don't know. But I think there is a fair bit of leeway.