These are words/short lines at the top or bottom of a column, that dangle alone awkwardly. A widow falls at the top of a column, separated from it’s previous paragraph.  An orphan can be either one opening line alone at the bottom of a page (the start of a new paragraph) or one word on the last line of a paragraph.  Orphans and widows create too much white space and look awkward.  Always proof read to catch these errors.