1. topsail - Noun
2. Topsail - Proper noun
In a square-rigged vessel, the sail next above the lowermost sail on a mast. This sail is the one most frequently reefed or furled in working the ship. In a fore-and-aft rigged vessel, the sail set upon and above the gaff. See Cutter, Schooner, Sail, and Ship.
Source: Webster's dictionaryThe ship had a smaller topsail on the mainmast above the mainsail and on the foremast above the foresail. Source: Internet
Thus the sail second up the mizzen-mast is the "mizzen topsail", and the third sail up the fore-mast is the "fore topgallant sail". Source: Internet
Gaff-rigged vessels may also have another sail, called a topsail, above the gaff. Source: Internet