Spacer

When a web page is "live," you cannot see the spacer. It's just there to let you add extra space to make it easier to place elements. As such, when you are editing, you can see the dotted box, which you can resize and move around. But once the page is "live," it is not visible to your visitors.

Below is a screen shot of what it looks like on your editing page (it's a really faded rectangle with a dotted border). The section it's in is colored so that it's easier to see, but it's not visible on the published web page. On this page, there is a spacer above this text, but you cannot see it. However, it makes it easier to place all the text further down the page. That's a spacer for you!