Link units help you limited Space

If you want ad units that adapt to your site and your readers' interests, consider link units. Each link unit displays a list of topics relevant to the content of your site, and when users click on one of these topics, they're brought to a page of AdWords ads related to that topic. Though you won't receive earnings for clicks on the topics, you'll be paid for user clicks on any of the AdWords ads on the resulting page.

See all link unit formats.

Link units are particularly effective for more focused content, where visitors tend to be seeking specific information. Their varied formats are space-efficient, too, so we recommend incorporating link units into new and unusual locations throughout your site. Remember that three link units per page can be placed in addition to the existing three standard AdSense ad units on that page.
To learn more about link units, please review the link units section of the AdSense Help Center.