in sea-language, a rope fastened to one or both the lower corners of a sail, to extend and retain it in a particular station. When a ship sails with a lateral wind, the lower corner of the main and fore sail are fastened by a tack and a sheet; the former being to windward, and the latter to leeward; the tack, however, is entirely diffused with a stern wind, whereas the sail is never spread without the assistance of one or both of the sheets. The stay-falls and studding-falls have only one tack and one sheet each: the stay-fall tacks are always fastened forward, and the sheet drawn aft; but the studding-fall tack draws the under clue of the sail to the extremity of the boom, whereas the sheet is employed to extend the inmost.