Gravatar (short for globally recognized avatar) is a free avatar centralization web service created by Tom Preston-Werner in 2005.
In computer science, the avatar is the representation of an Internet user. It can be in 2D, on social networks, forums, blogs or messaging software, or in 3D, for example in video games.
Since 2007, Gravatar belongs to Automattic, an American software publishing company founded by Matt Mullenweg in 2005. Automattic participates in the development and promotion of WordPress and offers other products and services (WordPress.com, JetPack, Akismet, etc).
Gravatar is supported natively in WordPress, it is mainly found in the comments. However, it can be used with other CMS or services. This is for example the case of Gmail.
On Gravatar, users create an account based on their email address, and associate an avatar (an image) to this account. Then when a visitor leaves a comment on a blog that asks for an email address, the site will ask Gravatar about the existence of an avatar linked to this address and will use it.