Section Targeting (Google)
"Section Targeting" is a feature Google offers which helps with one of the tricky problems in writing web site content. How is the search engine going to know which part of the page is the important content? To a human reading a web page it's obvious, but to the computer software running the search engine it isn't.
There's a rule of thumb people suggest to ensure the important content appears early within the data that makes the web page. But that's not always possible because depending on the way your pages are laid out.
Section Targeting lets the webmaster mark the sections of the page which are to be ignored, or the sections which are to be emphasized.
Implementation is very simple -- you insert into the page data comment tags containing specific text. See more information at the link above.