What is "gravatar"
Gravatar, globally recognized avatar (in English, Globally Recognized Avatar), is a service providing avatars via association to registered e-mail addresses, for a variety of sites, including those based on Wordpress. With Gravatar, your messages can be easily identified, on any site that uses the feature, by the image that represents you and that you have registered in the system.
In Gravatar, users can register an account based on their email, send an image to be used as an avatar and be associated with your account. Gravatar plugins are available for blog software, so when visitors post comments on the blog, the blog software checks to see if the email has an account in the Gravatar service. If you have it, Gravatar is shown in the user comment.