What is the usage of global:: keyword in C#?

Technically, global is not a keyword: it’s a so-called “contextual keyword”. These have special meaning only in a limited program context and can be used as identifiers outside that context.

global can and should be used whenever there’s ambiguity or whenever a member is hidden. From here:

class TestApp
    // Define a new class called 'System' to cause problems.
    public class System { }

    // Define a constant called 'Console' to cause more problems.
    const int Console = 7;
    const int number = 66;

    static void Main()
        // Error  Accesses TestApp.Console
        // Error either
        // This, however, is fine

Note, however, that global doesn’t work when no namespace is specified for the type:

// See: no namespace here
public static class System
    public static void Main()
        // "System" doesn't have a namespace, so this
        // will refer to this class!
        global::System.Console.WriteLine("Hello, world!");

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