In React.js, the angle brackets < > and </ > are used to define JSX (JavaScript XML) syntax. JSX is a syntax extension for JavaScript recommended by React for describing what the UI should look like. It looks similar to XML or HTML but ultimately gets transpiled to JavaScript.

Here's a brief explanation:

1. Opening Tag (< >): This is used to represent the beginning of a JSX element. It resembles an HTML tag but is used within JavaScript code.

    const element = <div>Hello, World!</div>;
   

   In this example, <div> is the opening tag of a JSX element.

2. Closing Tag (</ >): This is used to represent the end of a JSX element. It looks like an HTML closing tag but is used within JavaScript code.

    const element = <div>Hello, World!</div>;
   

   Here, </div> is the closing tag of the JSX element.

In JSX, you use these angle brackets to create React elements. The syntax is similar to HTML, but it allows you to embed JavaScript expressions within curly braces {}.

For example:

const name = "John";
const element = <p>Hello, {name}!</p>;

In this example, the value of thename variable is embedded within the JSX element using curly braces.

When React renders the JSX, it translates it into JavaScript function calls. For example, the JSX:

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

It gets translated into:

const element = React.createElement('h1', null, 'Hello, World!');

Conclusion:

This React.createElement call creates a React element with the specified type ('h1'), props (null in this case), and children ('Hello, World!'). The JSX syntax is just a more concise and readable way to create these React elements.