A footnote is a note or other text located at the bottom of a page of text, manuscript, book or statistical tabulation that provides comment on or cites a reference for a designated part of the text o [..]

also foot-note, 1841, from foot (n.) "lower end of a document" (1660s) + note (n.). So called from its original position at the foot of a page. Also sometimes formerly bottom note. As a verb [..]

explanatory note inserted at the foot of the page referring to a point within the text, usually indicated by symbols such as asterisks and daggers or by superior numerals.

A brief note at the bottom of a page explaining or expanding upon a point in the text or indicating the source of a quotation or idea attributed by the author to another person. Footnotes are indicate [..]

In typography, a reference relating to the main body of text positioned at the bottom of the page.

(n) a printed note placed below the text on a printed page(v) add explanatory notes to or supply with critical comments

Notation included in some GGT bus schedules to indicate a unique feature of a particular trip. Footnotes may indicate a trip doesn't operate on Sundays, for example.