It's an algorithm that decides placement of your products in the marketplace. The higher it is, the closer you get to the first page of a department or customer search. The scale is 0-10 and it is not static. You can move up and down it.
It seems to be a bell curve with most designers bunching up in the 4-7 middle. It is pretty easy to rise from 0-4 and hard to rise past 7. It is unknown exactly what decides your ranking but discussing it on the forum has led many of us to believe it is a combination of having various different products, doing some promoting (share products and/or collections to social media), not having royalty above 14.9%, having some collections. Doing this should get you up to 4. Rising higher than that will (I am pretty sure) require getting some sales. There is also speculation that the ratio of sold to unsold products is important. If you have thousands of products and only make a couple sales, you will rank low. If you sell most of what you make, you will rank high.
KeeganCreations
