Definition: As we know that every piece of code in .Net exists inside a .Net Type. Generally we put the code inside the class. The namespace is a collection of these classes or types. Every type exists inside a namespace. Namespaces can organize all the different types in the class library. Without namespace, these types would be grouped into a single long and messy list. In .Net the System namespace is stocked with several hundred classes. Also many namespaces are exists inside the System namespace. There are many namespaces that are must while developing a .Net application.
As we know a namespaces is a set of related classes. A namespace may also contain other namespaces. Today we will discuss about the System namespace. The System namespace contains the classes that most applications use for interacting with the operating system. You can refer to objects in namespaces by prefixing them explicitly with the identifier of the namespace. For example the System namespace contains the Console class, which provides several methods, including WriteLine.