In Visual Studio, a text template is a mixture of text blocks and control logic that can generate a text file. The control logic is written as fragments of program code in Visual C# or Visual Basic. The generated file can be text of any kind, such as a Web page, or a resource file, or program source code in any language. Text templates can be used at run time to produce part of the output of an application. They can also be used for code generation, in which the templates help build part of the source code of an application. (http://msdn.microsoft.com/en-us/library/bb126445.aspx)
Great! But in real life, how can we really use T4?