"The police force within the armed forces, responsible for dealing with members of the armed forces who break the law." (Cambridge Dictionary)
The graph displays the other subjects mentioned on the same pages as the subject "Provost Marshals". If the same subject occurs on a page with "Provost Marshals" more than once, it appears closer to "Provost Marshals" on the graph, and is colored in a darker shade. The closer a subject is to the center, the more "related" the subjects are.