ReactDOM

ReactDOM is an object or library in React that provides specific methods for interacting with the Document Object Model (DOM). It is used to render components, which are self-contained modules that output HTML. ReactDOM manages everything that gets added or removed from the DOM. One of the key methods provided by ReactDOM is render().

The render method takes two arguments, the component that needs to be rendered and the location (or DOM node) where it should be rendered. This allows you to control exactly where your React components get rendered in your HTML structure.

Here's an example of using ReactDOM:

```jsx
import React from 'react';
import ReactDOM from 'react-dom';

const element = <h1>Hello, world!</h1>;

ReactDOM.render(element, document.getElementById('root'));
```

In this case, ReactDOM is importing a single method, render(), from 'react-dom' library. The render() method then paints the DOM with the component, which in this case is a simple 'Hello, world!' header. The component is being attached to an HTML element with an id of 'root'.