Leaf lard is the highest grade of lard (lard is pork fat, the term is usually used to refer to rendered pork fat suitable for cooking). It comes from the visceral - or "soft" - fat from around the kidneys and loin of the pig. It lacks any real pork or meaty flavor, making it an excellent neutral-flavored cooking fat with a high smoking point.
Leaf lard is particularly prized by bakers for use in producing moist, flaky pie crusts.
Leaf lard can be tricky to track down. Some small butcher shops make and sell it. Rendering your own is quite simple if you can find the fat. Put the pork fat in a pot and gently heat it on the stove or in the oven until the fat is melted and any bits of meat are rendered out (they will be browned and crisp and delicious, by the way). Transfer the lard to a container with a sealable lid and store, chilled, for up to a month.