2.7 Content Holders
Content Holders can be used to re-use and populate the same page elements, or content snippets on more than one page or page template. Content holders can save you time and energy, and also allow you to update many pages in one place.
Keep in mind that when you edit the contents of the content holder, the changes are reflected on all the pages that share the content holder. For example, if you wanted google code injected on every page in the HEAD (the Head is not displayed content in the browser, it is used for loading scripts and setting variables for the page), then Content Holders make it a breeze.
This is more of a power user function, check out the video for more detail.