Global Objects

In React JS, a Global Object refers to an object that is available throughout the entire scope of the application. It is an entity that can be accessed from any file or component without needing to import or define it explicitly in every module. This global object exists in the global namespace and can hold methods or properties.

JavaScript already has certain built-in global objects such as Math, String, Date, etc. Additionally, browser environments have other global objects like window or document. In Node.js environment, there are also unique globals like __dirname or process.

Although Global Objects can simplify parts of your work, their usage is generally discouraged when it comes to React JS application development. The reason being it can lead to tightly coupled code and make unit testing a challenge.

A simple example of a global object in JavaScript (it's common usage, not specifically React):
```javascript
// Define a global object
var GlobalObject = {
name: 'My Global Object',
sayHello: function() {
return 'Hello, ' + this.name;
}
};

// Now, GlobalObject can be accessed anywhere in your code
console.log(GlobalObject.name); // Output: My Global Object
console.log(GlobalObject.sayHello()); // Output: Hello, My Global Object
```
In this case, `GlobalObject` is a global object, it can be accessed throughout all of your JavaScript code.

In ReactJS, you generally want to avoid global state, and pass props or use state management libraries like Redux, Mobx or React's built-in ContextAPI to manage the state of your application.