This article on the Plugin Hooks available in Version 2.1 of WordPress has now been split into two sections:
- Plugin API/Filter Reference - reference list of all of the Filter Hooks in WordPress
- Plugin API/Action Reference - reference list of all of the Action Hooks in WordPress
The reason for the aforementioned split is because Hooks are Actions and Filters. In fact, proper grammar would say "Actions and Filters can be Hooked."