The avatar is the users profile picture which is displayed inside the Author Box or next to a users comments. Below is an example of what the avatar looks like:

The avatar image is pulled from the Gravatar account associated with the users email address.

Border Radius

To change the border radius or rounding of the avatar, navigate to Appearance > Customize > Genesis Customizer > Content Area > Avatar. From here you will be able to adjust the border radius amount.