A sidebar is a square or rectangular box filled with a grey or lightly colored background. The text within the sidebar is either related to the main story, or a completely separate article.
For instance, if you were writing a story about a professor's new work of fiction, you could cite previous works in a sidebar, or if you have to fit several short articles on the same page, you could make one or two of them sidebars.
In the 1997 Freestone, sidebars simplified the layout of our faculty travel page.
Since Professor Mitchell's experience at Swansea was the main topic, we turned the shorter articles on Professors Palmquist and Krahnke into sidebars.
The sidebar is an indispensable tool, but if you overuse it, your newsletter will look too compartmentalized.