Wikipedia
Delmonico steak (or steak Delmonico) is a particular preparation of one of several cuts of beef (typically the ribeye) originated by Delmonico's restaurant in New York City during the mid-19th century. Controversy exists about the specific cut of steak that Delmonico's originally used.
Delmonico's steak may now, in the 21st century, refer to various cuts of beef steak, using preparations that vary regionally in the United States. Some of the steak cuts now commonly referred to as Delmonico steak include:
Boneless ribeye steak: A Delmonico cut ribeeye consists of two heart cuts of ribeye tied together with butcher's twine. It resembles a filet mignon in appearance, but because of the more marbled nature of a ribeye, is moister. The modern rarity of the Delmonico cut of ribeye may be because it renders the remaining pieces of ribeye unsaleable as anything but stewmeat, and the profit to be made from a pair of choice ribeyes is almost always more than that of a single Delmonico. The Delmonico Steak served by the current iteration of Delmonico's in New York is a boneless ribeye. Bone-in top loin steak: (a triangular-shaped, short loin cut, some suggesting the first cut of the top loin next to the rib end) also known as a club steak, country club steak, shell steak, and strip loin steak). Boneless top loin strip steak: (also known as a New York strip steak, Kansas City steak, strip loin, ambassador, boneless club, hotel or veiny steak)In addition to the steak, the original meal also included a potato dish, known as Delmonico's potatoes, prepared by making a mashed potato dish topped with grated cheese and buttered breadcrumbs, then baked until golden brown and served steaming.