Application variable is available to all classes in an ASP.NET application. Application state is stored in memory on the server and is faster than storing and retrieving information in a database. Unlike session state, which is specific to a single user session, application state applies to all users and sessions.

Create application variable

Application["Message"] = "Welcome to the Contoso site.";

Application variable when the application starts

Application["Message"] = "Welcome to the site.";
Application["PageRequestCount"] = 0;

Application variable with locking

Application.Lock();
Application["PageRequestCount"] = ((int)Application["PageRequestCount"])+1;
Application.UnLock();