What is namespace in c# ?

Namespaces in C# are used to organize classes.To access the class of a namespace, we need to use namespacename.classname. namespace is designed for providing a way to keep one set of names separate from another. The class names declared in one namespace does not conflict with the same class names declared in another. To define a namespace we need to use "namespace". eg.
  namespace NamespaceName
 { 
     class className
     {
     }
 }

 namespace WpfWorldNamespace
 { 
     class WpfWorld
     {
     }

 }
if we want to use WpfWorld class in another class then we have to add WpfWorldNamespace to that class by using Keyword.

using WpfWorldNamespace;
 namespace ExNamespace
 { 
     class Ex
     {
       var objWpfWorld = new WpfWorld();
     }

 }