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This article on the Plugin Hooks available in Version 2.1 of WordPress has now been split into two sections:
To learn more about what Filter and Action Hooks are, see Plugin API. For information about hooks in previous versions of WordPress, see Plugin API/Hooks 2.0.x.
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."
In WordPress Codex and source code, the terms "actions/filters" and "hooks" are sometime used ambiguously. See the Terminology Confusion note for clarity.