A footer is a bit of printed text at the very bottom of a page. The most common kind of footer is a page number.
In academic writing, page numbers are frequently formatted as footers centered at the bottom — or "foot" — of each page. When the page numbers of the novel you're reading are printed at the bottom of the pages, you can call those footers too. A footnote is different from a footer, although both come at the end of a page — footnotes appear less regularly, and each one is different, while a footer follows a regular pattern.