This is a behavior for CakePHP models. It makes it possible to generate unique URL slugs to be used in permalinks on CakePHP applications. This has been shown to help with search engine optimisation, getting important keywords and phrases into your site URLs.
Go from this:
http://example.com/posts/view/23
To this:
http://example.com/posts/view/great-new-widget-product-released
Quick overview:
* Specify a database field from which the slug should be generated (e.g. headline : 'The Great & the Good')
* Specify a field into which the slug should be stored when new records are created (e.g. url_slug : 'the_great_the_good')
* Automatically handles potential duplicates, and adds numerical suffixes accordingly
* Keeps slugs constant even when source field changes (for true permalinks, unlike the dynamic examples out there)
* Allows slug to be set manually instead of auto-generating it
For more information and a sample implementation
http://vduglued.com/2011/11/easy-cakephp-permalinks-and-url-slugs-with-sluggablebehavior/