footnote
n. countablen. a small note at the bottom of a page that gives extra information about something written above it. You usually see a tiny number in the main text that tells you to look down at the note.
n. an ancillary piece of information or citation placed at the base of a page, keyed to a specific part of the text by a superscript number or symbol.
The author explains the term in a footnote.
If you want to find the original source of that quote, check the footnote at the bottom of page twelve.
While the main text focuses on the political history of the era, a lengthy footnote provides a fascinating glimpse into the daily lives of the working class during that same period.
From foot + note.
Often used metaphorically to describe a person or event that is considered minor or secondary in history.