An Artist Overlay is a pop-up that appears when a customer clicks on your Minted artist name in the shopping areas of the site (e.g. on a category page like http://www.minted.com/wedding-invitations or on a product details page). Everyone with a product for sale has an Artist Overlay. For instructions on how to personalize your Overlay, see: How do I update my profile after my first win?
Here's an example of a gorgeous Artist Overlay, from community designer Laura Hankins.