Once, in the old days of the Internet, people would create hundreds of invisible anchor links at the footer of a webpage. These were keyword stuffed links. They did this so that they could rank for various keywords and get visibility in search engines for content their page wasn't even about.
But eventually most search engines got wise and began penalizing these types of sites severely. In fact, the punishments were so severe and far reaching that many web developers prefer to never place links at the footer of a webpage, so that the website is not automatically penalized by Google.