Oškvarky are made by cutting blocks of fresh pork fat into 1 inch cubes and cooking in a cauldron over a fire, constantly stirring until the lard has been rendered and the solid part of the fat and meat has turned into a crispy brown. Oškvarky can be enjoyed salted on their own as a high energy, crispy finger food, but can also be ground and used in traditional dishes such as pomazanka (spread for bread) and for pagac. See pagac recipe.
Crackling is technically the correct translation of oškvarky into English, but if you grew up in Chicago in the 1980’s, there is a nine out of ten chance that the word “crackling” means nothing to you. I find “crsipy pork fat” to be a better translation, because words need to have meaning in order to be understood.
www.SlovakCooking.com has a great article debating the pros and cons of using milk to make oškvarky.