Describe how to create and use custom REST API endpoints in WordPress.

Creating custom REST API endpoints enhances WordPress’ integration with external apps. Using register_rest_route in functions.php, developers can define custom endpoints and callback functions to handle requests, extending REST API to meet complex data requirements.

add_action('rest_api_init', function() {
    register_rest_route('myplugin/v1', '/data/', array(
        'methods' => 'GET',
        'callback' => 'my_custom_function',
    ));
});