Peking duck, pekin duck . . . goose! Only one letter separates a "Pekin duck" from a "Peking duck," so the terms are often used interchangeably. But one paltry letter can be a big poultry difference; these words are both descriptors of ducks, but they're definitely not the same!
A Pekin duck is a breed of duck. Also known as a Long Island duck, this domesticated descendant of the Mallard has a yellow bill, white plumage, and orange webs and is the most popular commercial duck breed in America, where they're raised primarily for egg and meat production.
Peking duck originated in Nanjing, and the first ducks used to prepare the dish were small birds with dark feathers. Incidentally, these days, most Peking ducks are prepared using Pekin duck. How's that for irony?