This term is also often defined as W.O.P. or Without Papers.

During the beginning of this century, Italians flocked to New York City following the American dream. To them, it was very important to be American, and be a part of this country even if it meant living ten to a room in a tenement house and sharing one bathroom with five-hundred other people. To say one was Without Papers was essentially calling them a border jumper and expressing the belief that they were not, in fact, American at all. Every male member of my family since my Great Grandparents arrived, at one time or another, has cracked skulls for being called this name except for my generation. I find no insult in it at all, but then again I don't find being called "un-American" all that insulting either. Though I hold no sentimental notions of my glorious American heritage, I do have a bit of nostalgic spot for my family and what they endured to get here, be happy and successful in their lives; from that point of view it isn't hard to see how them's fightin' words.