To what does the footnote refer?
In formal writing the footnote refers to any material that is not your own. If you borrow, paraphrase, or quote from someone else you can cite the material in a footnote. Each citation style (MLA,APA, Chicago) has its own rules on whether to use footnotes or endnotes, but as a rule of thumb, footnotes are used for ease of reading. If you write a long essay and have to insert some additional information that doesn't fit into the flow of your essay but should be mentioned, place it in a footnote for the reader to see. If you are writing for college, ask your professor whether he/she would like footnotes or endnotes. For instance, if your citation style is MLA ( Modern Language Association), your paper should technically be formatted containing endnotes in addition the Works Cited list, but many professors ask specifically for footnotes. I think this trend has perhaps to do with the fact that many professors now request electronically submitted papers and endnotes do not require scrolling to the end of the document.