"Footnote references" are small notes or numbers that are added at the bottom of a page in a book or document. These references provide additional information or sources for the content that is on the page. Full definition
For example, being able highlight and annotate the book without ruining it in the process, or being able to research footnote references with a single click rather than having to manually find the resource and look it up. (pcworld.com)
Far better for the Canadian legal profession to use Halsburys Laws of England with a few footnote references to Canadian cases in what was known as the «Canadian Converter», and major legal treatises from the U.K., than to use the obviously inferior publications that would be written by Canadian authors. (slaw.ca)
Adam Smith mentions Jesus only once in Wealth of Nations, in a footnote reference to the «compagnie de Jesus.» (firstthings.com)