The {url} is a brand new keyword which can be used in the designer to indicate the local web-site url, instead of having to write the whole SharePoint site/sub-site path.
Important Note:
Up to this point, when you had to create a new List Query using PowerForm's designer, you had to enter the full path to the Site Url property. E.g.
Using the new {url} keyword, you can now accomplish the same thing with less effort. E.g.