In WordPress, the term “footer” generally refers to an area or section of a webpage that is usually displayed at the bottom (or “foot”) of a web page.
By default, WordPress begins with a footer section at the bottom of every webpage that includes information about the current version of WordPress that is being used. As an administrator, you can choose what appears in the footer, including text, copyright information, menus, advertisements, and/or widgets. In some cases, scripts may also be stored in the footer area.
For designers, the layout information and contents of the footer are usually included in the file “footer.php” inside the template directory.
It must be understood that footer is just a label for a given piece of screen real estate and a footer section can be displayed anywhere, not only at the bottom of the page.
Best practices are to only place information in the footer section that is relevant to the entire website, not a specific post or page. For example, your copyright information applies to the entire website and so should be placed in the footer section.
Note: It is possible for a WordPress site to have multiple footers depending on the theme that you are using. Generally, however, most WordPress sites have a single footer that displays the same across all web pages.
The opposite of the footer section is the header section which usually is displayed at the top of a WordPress website.