Final answer:
The content that displays at the top of every page in a document is known as a header. It can include information such as the title, author's name, or page number, and should not be confused with footers, style sets, or the document's title.
Step-by-step explanation:
The document content that displays at the top of every page is called a header. When you add a header to a document, whether it be a word processing document or a web page, the same content will appear at the top of each page. This is useful for including elements such as the document's title, chapter name, page number, or the author's name. Unlike the footer, which appears at the bottom, the header is always at the top. Headers are not to be confused with the style sets, which define the overall look and formatting for a document, or the title, which is generally the name of the document and does not necessarily appear on every page.