It's a free service from Goggle. It's basically a way of tracking traffic to your shop, website, blog, etc. It shows you where your viewers are coming from, both what countries and what websites. It's a great way for you to see what items are attracting attention and what is being ignored for the most part.
Etsy has a way of using it in conjunction with your store. Here's the link to their blog post about how to get it set up.
http://www.etsy.com/storque/etsy-news/tech-update-etsy-web-analytics-now-available-3141/