Master pages are an ASP.NET 2.0 feature that both Windows SharePoint Services 3.0 and SharePoint Server use extensively.
Master pages have the same structure as normal pages; however, their file names have an extension of .master instead of .aspx.
Use master pages to control the general layout of pages, and use cascading style sheets to apply common styles to elements on each page in a site.
Windows SharePoint Services 3.0 provides a global default master page, a global meeting workspace master page, and a number of administration master pages. Administration master pages are applied to pages that include _layouts in their URL.
SharePoint Server provides the same master pages as Windows SharePoint Services 3.0, plus a number of custom master ...