.NET Framework 2.0 introduces the concept of Partial classes. Partial classes allow you to split a class definition across multiple source files. Separation of class definition facilitates multiple programmers to work on the same class simultaneously and/or better organization of code within a class. VS.NET 2005 uses this concept to hide designer-generated code when you create Windows Forms.
To create a partial class, add the “partial” keyword to the class definition. To learn more about partial classes, read the MSDN library article mentioned below or visit this link. Though the links point to C#, partial classes are available in Visual Basic also.