The additional information included in the bottom margin of your paper is called a

Footnote is the additional information included in the bottom margin of the paper. It is usually added to the paper to cite a reference without committing plagiarism. It can quote part of the reference or just the citation, in APA or MLA (depending on your choice). However, a footnote can also be used in making comments about the ideas presented in the paper. In this way, the reader can read the main text ad go directly to the footnote to read your reaction.