Fat from around the pig's kidneys is the "cleanest," meaning that it gives the purest fat without many other bits and pieces. If you experiment with making lard from different pig parts, you'll soon notice that leaf lard is the whitest and mildest. Leaf lard's mild odor and almost-not-there taste impose the least on the flavors of whatever you're cooking, while at the same time, doing an excellent job as a cooking fat.