By default, Piwik will report your Page URLs and Page titles in ‘categories’, automatically constructed based on the slash character / as a delimiter.
For example, a Page with a URL “http://example.org/about/contact” will be reported under the category “about” in the Page URLs report. When you click on it it will open the pages inside this category, and show the stats for the subpage “contact”. This feature is very useful because it helps visualize which sections of your website have the most traffic, rather than having all your page URLs at the same level.

This grouping feature is also very useful with Page Titles. You can use it for tracking custom flash events (“game / clickStart”, “game / registerNewUser”), video events (“videos/ bestOf2011 / start”, “videos/ bestOf2011 / pause”), simply organize your pages into a easier to analyse structure, etc.

In the Piwik Javascript tracking code, you can specify custom page titles by calling piwikTracker.setDocumentTitle() (Learn more about the JS Tracking API). For example, to track a custom page view when a user clicked on a button in your web app, you could write

piwikTracker.setDocumentTitle("ajax/click view button");
piwikTracker.trackPageView();

You can also customize the delimiter to use for splitting your page URLs and Page titles into categories (or disable the feature by setting the delimiter to a character not in use in your Page titles). Edit your config/config.ini.php file, and set the following:

[General]
action_title_category_delimiter = ::

You can then define your custom page names as follows:

piwikTracker.setDocumentTitle("Products :: Gardening :: Seeds id=123");

and your pages and categories will be grouped according to the :: delimiter.