Ambassadors mainly exist to welcome new members to a particular forum, answer questions, be active in FAQ threads etc. - essentially helpful and knowledgable participants of a given forum who commit to contributing to the forum and making it a friendlier place. (YouŽll see that Ambassadors mostly exist in large forums which can be a little overwhelming for new members).

Moderators have a more formal role in ensuring that the forum is kept "tidy". Duties include editing/deleting/merging posts/threads, taking care of reported posts and taking disciplinary action if necessary - essentially all the stuff that are little fun, but need to be done.

While many moderators also happen to be very knowledgable and helpful, it is not a requirement. Many mods will at least try to browse through all active threads and also answer individual questions (which is more than mods are expected to do), but a few mods make it clear that their only job is to enforce the T&C. In those instances ambassadors may come in very handy.