In JavaScript, the global namespace refers to the global scope or the highest level of scope in a program. It is the space in which variables, functions, and objects are defined outside of any function, class, or block. Any variable or function defined in the global namespace can be accessed from anywhere in the program.

When a JavaScript program is executed, a global object is created that serves as the container for all variables and functions in the global namespace. In a web browser environment, the global object is the window object, which represents the browser window.

Variables and functions defined in the global namespace can sometimes cause naming conflicts or unintended consequences when used in different parts of a program. To avoid this, it's generally recommended to use more specific namespaces or modules to organize and encapsulate code.