A footer is the caboose of any given site. Similar to the header, the footer stays the same page to page, but it appears at the very bottom of every single page of the website rather than the top. A footer is typically a very structured section of the site that serves as the last opportunity to get various information to your site visitors.
Some organizations opt to keep this as simple as possible, with only copyright information. Some create large footers, repeating the primary navigation, a call to action or two, and a statement that they are a 501(c)3 to help build credibility. Social media links are another popular item for website footers.