Every macro package gives some way to manipulate the headers and footers (also called titles) on each page. This is text put at the top and bottom of each page, respectively, which contain data like the current page number, the current chapter title, and so on. Its appearance is not affected by the running text. Some packages allow for different ones on the even and odd pages (for material printed in a book form).
The titles are called three-part titles, that is, there is a left-justified part, a centered part, and a right-justified part. An automatically generated page number may be put in any of these fields with the ‘%’ character (see Page Layout, for more details).