What is the key characteristic of a 'widow' in typesetting?

In typesetting, a 'widow' refers specifically to a single word or a very short line that appears at the end of a paragraph. This layout issue can disrupt the visual flow of text, creating an imbalance or awkwardness in the spacing between paragraphs. Designers often seek to avoid widows because they can detract from the overall aesthetic and readability of the text. Correctly managing text flow to eliminate widows helps to create a more polished and professional appearance in printed and digital materials.

The other options describe different typographic issues or concepts but do not accurately define a 'widow.' A line that is too short might relate more to general text alignment or justification concerns, while a word isolated at the beginning of a new column pertains to a different typographical problem known as an 'orphan.' Similarly, a brief sentence without context, while it could be an issue of clarity or coherence, does not fit the specific definition of a 'widow.'