the.com/covered wagon

means A horse- or ox-drawn wagon with a curved canvas top stretched over wooden hoops, used to haul families and belongings across overland trails.

from The thing predates the term's casual use: the canvas-roofed farm and freight wagon was common well before westward migration, often called a 'prairie schooner' for the way its white cover billowed like a sail above the grass. 'Covered wagon' is simply descriptive — cover plus wagon — with 'wagon' itself tracing back to Dutch 'wagen,' a cousin of 'wain' and 'vehicle.' The phrase stuck hard to American memory largely through 19th-century overland trail migration and later through Western films and novels, which cemented the image long after the real wagons had rattled into history.