A topselot is a type of sail used on sailing ships, specifically on square-rigged vessels. It is the third sail up from the deck on each mast, located above the mainsail and topsail. The topselot is a smaller sail compared to the sails below it, and it serves to catch wind that may be higher up and to improve the ship's overall sailing performance.
Topselots are typically made of a lightweight canvas material, and they are hoisted and lowered using ropes and pulleys. They can be adjusted independently of the other sails, allowing the crew to optimize the ship's sail configuration according to the wind conditions. When the wind is favorable and the ship is sailing close-hauled, the topselot can be extended to increase the sail area and capture more wind. In stronger winds or when the ship is tacking, the topselot can be reefed, which means that a portion of the sail is rolled up to reduce its size and improve control.