MO Auto add terms is a Drupal 6.x module that automatically assigns terms to your pages from their contents, titles, and comments. This makes it very useful to build a complete site index without worrying about missing a few terms here and there. It also allows you to offer tagging functionality to your users, even when you prevent them from adding terms (by hiding the taxonomy field), and yet have terms assigned to their posts. This assignment is done automatically with MO Auto add terms. The module can also add parent terms, remove terms that are not in the page anymore, recognize equivalents and synonyms, hide the taxonomy selection box from the edit page, limit the number of terms to add automatically, etc.