Conditional rendering is a feature in React that allows developers to control what gets displayed on the screen based on certain conditions. This means that certain parts of the user interface can be shown or hidden based on the state of the application. In other words, the rendering of a component can depend on the value of its props or state.

One common use case for conditional rendering is to show or hide certain information based on whether or not a user is logged in. Another use case is to render different components based on the device the application is running on. For example, a mobile app might render a different navigation bar than a desktop app.

To conditionally render content, developers can use the ternary operator or the logical && operator. The ternary operator is similar to an if-else statement, while the && operator is used to render content if the condition on the left-hand side is true.

Here's an example of using the ternary operator to conditionally render content based on whether or not a user is logged in:

function Greeting(props) {
  const isLoggedIn = props.isLoggedIn;
  return (
    <div>
      {isLoggedIn ? (
        <h1>Welcome back!</h1>
      ) : (
        <h1>Please log in.</h1>
      )}
    </div>
  );
}
```.

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