The using keyword has two major uses:
As a directive, when it is used to create an alias for a namespace or to import types defined in other namespaces. See using Directive.
As a statement, when it defines a scope at the end of which an object will be disposed. See using Statement.
In addition, the using static directive lets you define a type whose static members you can access without specifying a type name.
See Also
C# Reference
C# Programming Guide
C# Keywords
Namespace Keywords
Namespaces
extern



