Image of a Brig type of sailing ship. Brigs have two masts (i.e., tall vertical poles) containing fully “square-rigged” sails. The term “square-rig” comes from the way the sails are configured. Each of the two masts on a brig contain one or more long wooden poles (called spars) which are horizontally attached (i.e., “square”) to them. Attached to each spar (also called “yards” – jeez, so many terms) is a four-cornered rectangular canvas sail.
Image is from Plate 4 of the book: “Text-Book of Seamanship: The Equipping and Handling of Vessels Under Sail or Steam. For the Use of the United States Naval Academy”, 1884, by Commodore S. B. Luce, U. S. Navy.