Other forms: zarfs
A zarf is something that helps you hold a hot cup without burning your fingers. Don't leave the coffee shop without your zarf!
Zarf is a peculiar looking word that is a loaner from Arabic and originally denoted a metal holder for a drinking glass — which would be unwieldy to handle if it contained a hot beverage. Now in the latte age, zarf is extended to denote any such cup-holding appliance, like the collapsible cardboard ones you get for paper cups to hold your skinny double mochachino.