"A woman whose husband or wife has died and who has not married again." (CD)
See also: https://dictionary.cambridge.org/us/dictionary/english/widow
The graph displays the other subjects mentioned on the same pages as the subject "Marital Status--Widows". If the same subject occurs on a page with "Marital Status--Widows" more than once, it appears closer to "Marital Status--Widows" on the graph, and is colored in a darker shade. The closer a subject is to the center, the more "related" the subjects are.