The Global.asax file, also known as the ASP.NET application file, is an optional file that contains code for responding to application-level and session-level events raised by ASP.NET or by HTTP modules. The Global.asax file resides in the root directory of an ASP.NET application. At run time, Global.asax is parsed and compiled into a dynamically generated .NET Framework class derived from the HttpApplication base class. ASP.NET is configured so that any direct URL request for the Global.asax file is automatically rejected; external users cannot download or view the code in it. The Global.asax file is optional and is needed only if there is application or session events.to be handled.
Global.asax Syntax
Tags of Global.asax file are
Application Directives: Tags that define optional application-specific settings used by the ASP.NET parser when processing the Global.asax file.
Code Declaration Blocks: Tags that define sections of server-side code that can be embedded in the Global.asax file.
Code Render Blocks: Tags that define inline code or expressions that can be embedded within the declarative sections of the Global.asax file.
Server-Side Object Tag Syntax: Elements that create application and session variables using a declarative syntax.
Server-Side Include Directive Syntax: Tags with a syntax for specifying server-side includes of text files within ASP.NET application files.