routing is a technique that a user request a path that allows you to map the physical path of the action method.for example:a user requests a view http://www.somewebsite.com/home/viewdata that doesnt exist on our action methods. we have only http://www.somewebsite.com/home/data action. simply we write a route table and map the user requested viewdata action to data

http://msdn.microsoft.com/en-us/library/cc668201.aspx

http://www.asp.net/mvc/tutorials/older-versions/controllers-and-routing/asp-net-mvc-routing-overview-cs