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:
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