What is a footnote?

A footnote is an ancillary piece of information printed at the bottom of a page that provides additional context or clarification about the main text. This can include citations of sources, explanations of terminology, or other relevant details that enhance the reader's understanding without interrupting the flow of the main content. By placing this information at the bottom of the page, it allows the reader to continue reading without significant disruption while still having access to important references or elaborations that support the text above.

The other options may describe related concepts but do not accurately represent what a footnote is. Illustrations at the bottom of a page serve a different purpose, summarizing content or providing a visual component rather than supplementary text. A section summarizing the text above focuses on condensing information and is typically found at the end of a chapter or article rather than as a sidebar note. An index, on the other hand, lists terms and topics of interest within the document, allowing readers to find specific information, but it is not the same as a footnote.