Lard is the rendered fat of a pig. At room temperature, it is pale white in color and solid. It is sold in blocks similar to butter.
In Britain during WWII, butter was in very short supply and severely rationed, so lard (which keeps well even at room temperature) started to be used in its place.
Although lard was originally used as a frying medium, over the years many recipes have been created using lard as an ingredient. Traditional British delicacies made from lard include lardy cakes and "lardy bombers", pastry cases filled with seasoned lard and deep fried.