MasterPage: master pages allow you to create a consistent layout for the pages in your application.
A master page is an ASP.NET file with the extension .master.The master page is identified by a special @ Master directive that replaces the @ Page directive that is used for ordinary .aspx pages. The directive looks like the following.
<%@ Master Language="C#" %>
Content Pages: You define the content for the master page's placeholder controls by creating individual content pages, which are ASP.NET pages (.aspx files and, optionally, code-behind files) that are bound to a specific master page. The binding is established in the content page's @ Page directive by including a MasterPageFile attribute that points to the master page to be used.
<%@ Page Language="C#" MasterPageFile="~/MasterPages/Master1.master" Title="Content Page"%>
