Lard is fat (the thick oil, not the fat tissue) from a pig. Unlike normal shortening, which can be used as a lard substitute, lard is free of trans-fatty acids. Lard is also lower in saturated fat than butter, making lard one of the best of the well-known solid fats. Lard is slightly softer than Crisco shortening.
Lard is particularly important for traditional pie crusts, such as the one for apple pie. Lard gives the desired flakey texture. Substitution is not advised. Lard also makes for better biscuits, and can be used in roast potatoes.
Lard does not last quite as long as shortening does. Refrigeration will help. Refrigeration is a good idea anyway, because the pastry-like foods commonly made with lard will turn out best if everything (ingredients, air, rolling pin, work surface, bowls, etc.) is kept cold until baking.
Larding is the process by which lardons (bits of lard) are injected into meat. This is sometimes done before cooking a tough piece of meat.
Lard can be produced by baking a pork roast, preferably with some cuts in the fat tissue to let the lard drain out. If the drippings are allowed to sit in a tall glass container, lard will float to the top. Be sure to allow enough time for the non-lard content to settle out; reheating may be required. Once settled, the lard must be refrigerated. Home-made lard can have a bit of a roast pork flavor, which is very good for making refried beans.
Bacon grease is essentially lard.