Bacon renders -- or gives up -- its fat when cooked over low to medium heat. Cooking the bacon melts the fat, which separates from the connective tissue and meat, and becomes what is otherwise known as bacon fat.
Rendering is also used to describe what happens when butter is clarified -- meaning heated until its milk solids separate and can be removed -- as well as the process of turning suet into tallow and pork fat into lard.
Recipe: Braised Mustard Greens With Bacon And Shallots (Cookthink)
Reference: Do I need to blanch bacon before using it in a recipe? (Cookthink)