A firm support, usually wood, board or metal, it is used as a painting surface. Many artists prefer to use panels because they are stronger and more rigid than canvas. Before the fifteenth century when artists began using canvas, most paintings were done on panels, especially wooden panels that were sized or covered with a solution that sealed the pores. Source: Kimberley Reynolds & Richard Seddon, "Illustrated Dictionary of Art Terms"<br><br>One page of a brochure, such as one panel of a rack brochure. One panel is on one side of the paper. A letter-folded sheet has six panels, not three.