A tall ship, by definition, is a sailing vessel whose masts are in segments, made up of several timbers in order to give strength, and to make each mast more manageable for partial removal and repairs. The Lady Washington is a tall ship because her masts are each in three sections--lower, and topgallant--joined by caps.

a big sailing ship of traditional design, the kind of ship that opened the whole world to human intercourse and brought the divided branches of mankind together,'' he said

a large square-rigged sailer carrying three or more masts)

a large traditionally rigged sailing vessel

a meaningless term for people who are serious students of ship history,'' Blanchard insisted

a traditionally rigged sailing vessel differentiated from modern sailing vessels by her topmasts and topsails

Tall ship is an informal collective term for some kinds of sailing ships. Contrary to other sailing ship classification terms, tall ship does not describe a particular kind of sailing ship identified by a sail plan — both barques and brigantines, for instance, are tall ships.