Addon Views are a new concept in Tiki introduced with Addons. Addon Views are the way to run custom code in your Addon and have the output shown within Tiki.
You can create as many views as you want for your addon, each of which is a php file containing a php function of the same name as the php file. For example, the file helloworld.php must contain a "function helloworld()". See A Hello World Addon for more comprehensive example of using a View.
The output of a View can be displayed within Tiki through the wiki-plugin PluginAddon. Normally, you would using the Addon plugin within pages that are created by Profiles in the Addon.