The document discusses namespaces in .NET. Namespaces provide a logical grouping for classes, interfaces, and value types. The .NET Framework includes several key namespaces like System, System.Collections, System.Data, and more. Each namespace contains related classes that provide common functionality, such as basic data types, collection classes, database access classes, and more. Namespaces help avoid naming collisions and provide organization within large class libraries.

1. NamespacesAbstract container or environment created to hold logical grouping of classesIt is like header files in C, C++

2. .NET Framework class libraryClassesInterfacesValue types

3. NamespacesCLASSMETHODUnique Name(Namespace)CLASS1CLASS2METHODMETHODCLASS3CLASS4METHODMETHOD

4. NamespacesSystem

5. Used by all applications

6. Classes represent the basic data types which were presented earlier in the Common Type System System.CodeDom