Thank You Commenter is a drupal module which sends a mail to the person who comments on nodes. Now the question comes what is Comment & Node?
So here is the answer :
Node - Most of the content on Drupal websites are stored as well as treated as "nodes". A node could be any posting, such as a poll, article forum topic, blog entry etc.. If we treat all the content as nodes then it allows us the flexibility for creating new content type and to painlessly apply new features or changes to all content.
Comments - A post done by the user to discuss a forum topic, a book page, etc is called Comment. We do not store comments as nodes but these are always tied to one. If Filters, smileys and HTML that work in nodes are configured accordingly then it will also work with comments.
This module works for both logged in users and anonymous users. Logged in users are basically authenticated users or we can say registered users into a particular site on which they are working whereas anonymous users are the one who are not registered to it.
This module have stable drupal6 release and development release in drupal7. So it works in such a way that whosoever comments on node, a thank you mail goes to that person containing the node url of that comment. Also the mail contains the url of site and name of the user as well. As mail also contains the url of node on which the user has commented thats helps him to keep the track.