Strutto is reconstructed pork fat; it's a semi-solid, white, waxy mass made by slowly melting the fat, straining through a cloth and refrigerating it. It is used as an ingredient in some Italian recipes, for frying, and for killing your husband slowly over several years, while he unwittingly praises your cooking skills.
Nowadays many traditional recipes replace it with butter because strutto is not a healthy thing to eat. Have you ever heard of "good cholesterol" vs. "bad cholesterol"? Well, strutto is as bad as it gets; it's the Adolf Hitler of cholesterol. It easily gets rancid if exposed to air, turning yellow and acquiring a disgusting, peculiar smell.
Since it is a low-cost fat, it's often used in bread, breadsticks and similar, much to the chagrin of nutritionists.
100 g of strutto contain 900 calories and 82 mg of cholesterol.