According to MSDN, "The Global.asax file, also known as
the ASP.NET application file, is an optional file that contains code for
responding to application-level events raised by ASP.NET." The Global.asax
file is parsed and dynamically compiled by ASP.NET into a .NET Framework class
the first time any resource or URL within its application namespace is
activated or requested. Whenever the application is requested for the first
time, the Global.asax file is parsed and compiled to a class that extends the
HttpApplication class. When the Global.asax file changes, the framework reboots
the application and the Application_OnStart event is fired once again when the
next request comes in. Note that the Global.asax file does not need recompilation
if no changes have been made to it. There can be only one Global.asax file per
application and it should be located in the application's root directory only.