Robert Bringhurst, The Elements of Typographic Style, (p.43–44):
The typographic terminology is telling. Isolated lines created when paragraphs begin on the last line of a page are known as orphans. They have no past, but they do have a future, and they need not trouble the typographer. The stub-ends left when paragraphs end on the first line of a page are called widows. They have a past but not a future, and they look foreshortened and forlorn. It is the custom — in most, if not all, the world’s typographic cultures — to give them one additional line for company.