It is rendered from the pork fat, the quality of which varies depending on where the fat comes from on the pig, but it has been a traditional cooking fat or shortening for centuries. Hey, the fat left over from frying bacon is lard and we know how good that tastes.
However, it became unfashionable when vegetable oils were introduced and the health risks associated with using animal fats became a concern because of its high fatty acid and cholesterol content.
Lard is though still used in baking for making such products as lardy cakes and hot water crust pastry for pork pies.
Even as recent as the 20th century lard has been used like butter or as a butter substitute in Europe ( I remember seeing Antonio Carluccio on the TV simply spreading lard onto a piece of bread to make a sandwich somewhere in Italy, but then I guess its only like eating dripping on a sandwich) and North America. It is said to contain less saturated fat and cholesterol and more unsaturated fat than an equivalent weight of butter.
Unlike many margarines and vegetable shortenings, unhydrogenated lard contains no trans fat and for this reason its making a bit of a comeback as a replacement for partially hydrogenated vegetable fats.
It does of course, because it comes from the pig, have religious dietary restrictions and for this reason a lot of commercial bakeries have replaced lard with beef fats and if you are in the hospitality or catering profession you will need to be sensitive to your customer requirements in this respect.