You want to know more about the Default blocking settings in K9 Web Protection.
The Default Protection Level blocks a collection of categories, which Blue Coat calls the 'Commonly Blocked Categories' but allows Unrated Sites. These categories are what are generally considered objectionable to family viewing.
Commonly Blocked Categories
To view a list of the commonly blocked categories, log into the K9 Administrative Interface (which is accessible through your Start menu). Once in the K9 interface, click Setup. When the Default level is selected, you can see a list of the categories blocked by that setting. Within that list you can click on any of the categories to get more information on what types of sites are included in the category.
Unrated sites are websites that are not yet assigned to a K9 category, and for which Blue Coat's Dynamic Real-Time Rating system cannot yet determine a rating.