A butternut is also known as a white walnut, and is grown only in this country (and apparently mostly in a swath stretching from New England through Indiana to the upper Midwest). It has a rich, oily meat. It is generally used in baking and candy making. Because of its high oil content, it will go rancid fairly quickly, so store it in your freezer until ready for use. You can certainly substitute it for other nuts in your cooking projects