What role does mod_rewrite play in dynamically generating URLs for web pages in PHP?

Mod_rewrite is a powerful module in Apache that allows for URL rewriting, which can be used to dynamically generate clean and user-friendly URLs for web pages in PHP. By using mod_rewrite, you can transform URLs that are easy for users to understand and remember, while also improving SEO and making your website more user-friendly.

```php
RewriteEngine On
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(.*)$ index.php?url=$1 [QSA,L]
```

In this code snippet, we are enabling the mod_rewrite engine, checking if the requested file or directory does not exist, and rewriting the URL to pass it as a parameter to the index.php file. This allows for dynamic generation of URLs in PHP based on user-friendly input.