What is the purpose of the `header('Location: URL')` function in PHP?

The purpose of the header('Location: URL') function in PHP is to redirect the user to a different URL. When this function is called, it sends a specific HTTP header to the client indicating that the requested resource has been moved to a new location, which is specified by the URL provided. This action effectively instructs the web browser to navigate to that new address.

Redirecting users is a common practice in web applications for various scenarios, such as after form submissions or when a page has moved. It effectively changes the current URL in the browser's address bar without requiring additional input from the user.

The other options relate to different functionalities within PHP. Setting the content type of the response pertains to informing the client about the type of content being sent to them, which is not the primary functionality of the header function with the Location attribute. Ending a session and defining a new variable do not involve URL redirection and are associated with session management and variable creation, respectively.