What are the best practices for passing variables between pages in PHP, especially in the context of search result pages?

When passing variables between pages in PHP, especially in the context of search result pages, it is best practice to use sessions or URL parameters. Sessions can store variables across multiple pages for a single user session, while URL parameters can pass variables through the URL. This ensures that the variables are accessible on the subsequent pages.

```php
// Start a session to store variables across pages
session_start();

// Set a session variable with the search query
$_SESSION['search_query'] = $_POST['search_query'];

// Redirect to the search result page
header('Location: search_results.php');
exit;
```
In the search_results.php page, you can retrieve the search query using `$_SESSION['search_query']` to display the search results.