Application page is an ASP.NET Web page that is designed for the use of SharePoint Web site. Application pages are a specialized type of ASP.NET page. The primary difference between an application page and a standard ASP.NET page is that an application page contains content that is merged with a SharePoint master page. A master page enables application pages to share the same appearance and behavior as other pages on a site. Application pages are shared across all sites on the server, whereas a site page is specific to one site. Application page Only deployed by farm solution and Required farm administrative  privileges to deploy. Application page Only support server controls or user controls. They have code behind or inline code. When we create an application page, add an Application Page item to a SharePoint project. When you create an application page, Visual Studio adds to  the following folders to your project: Maps to the _layouts virtual directory of the SharePoint file system.   Contains the files that make up the application page. By default, this folder has the same name as your project. You can rename this folder at any time. When you run the project, Visual Studio deploys this folder to the _layouts virtual directory of the SharePoint file system.   Open visual studio 2012, click on new project select SharePoint solutions under the office/SharePoint from which select project type as SharePoint 2013- Empty Project. Enter the project name and click on Ok. Select the our sharepoint site url and check the farm solution  and Finsh. Right click on project soluction, Add  and Add New Item. Select the application page and enter the page name, click ok button   Now we can see our application page was store in under layouts folder