Liquid Template Variables - handle
From Spiffy Stores Knowledge Base
The handle of an object is used to refer to the object in the web site URL or address.
By default, the handle is the object's title with all spaces being replaced by dashes.
For example, "My Brand New Product" would have a handle of my-brand-new-product and this would appear in the URL as
http://www.myshop.com/products/my-brand.new-product