Definition: In magazine writing, a sidebar is simply a shorter piece that accompanies a longer article. A sidebar can be anywhere from a few senetences to whole other page, and may compliment or contrast the article it's placed with. Good ideas for sidebars include a dissenting opinion, resources for further information, a true life applicable story that goes with the article, or an experts viewpoint.
Also Known As: May be called a filler at times, although it is generally the responsibility of the original article's writer, and is part and parcel of the assignment.
I included a sidebar detailing where you can buy the items recommended in my article.