Gravatar stands for Globally Recognized Avatar. Users can set their avatars at http://gravatar.com/ and they will be displayed alongside their comments in any website that supports them.

To enable gravatars in your WordPress comments, you can install the WP-Gravatar plugin. Once you activate it, the gravatars will be displayed next to the users that have commented your posts. In addition, you can set a custom image to be displayed if the user does not have a gravatar account.

If you enable gravatars on your website, you can allow users to post comments without being registered. At the same time you will be able to recognize regular visitors through their gravatars.

Note that gravatars match the e-mail that users have registered with. Therefore, if someone sets his/her e-mail as yours, you will see your gravatar next to his/her posts.