WordPress has designated areas that developers can leverage within their plugin; these areas are rightfully named Hooks. Currently, the two types of hooks available are Actions and Filters.

An Action is a hook that's triggered during common blogging events such as creating a post or deleting a comment. For example, the publish_post action is triggered whenever a post is finally published. Similarly, the wp_insert_comment is fired each time a website visitor leaves a comment.

A Filter, like an Action, is a hook that plugin developers use to modify various types of data before it's added to your database or displaying it to the end user. For example, the the_content filter is applied whenever your blog renders a "Posts" content. The content_save_pre filter is applied right before a blog post's body content is saved to a database.

You can learn more about Actions, Filters, and WordPress Plugins in general at: