The Clipper is a fast, four-masted trade ship with an increased cargo hold.
Clipper ships are the kings of trade. Even once steam ships begin to appear, clippers remain much more economical to run, and if the wind is right, no other surface vessel is faster. These ships are the tool of choice for a trade route from the New World to the Old, or vice versa--with a four-slot cargo hold and less slowdown from a full load, they can keep your cities fed with little trouble. Compared to a Schooner, a clipper has enough health to survive harassment and the speed to escape any foe it might run into--but not for long. Gunboats are especially dangerous for clippers, since they can fire without turning and can keep up just long enough to deal enough damage to slow them down. Clippers are also good choices for early Expeditions due to their large holds, but their lack of other inherent statistics leave them behind fairly quickly.
Do note that Pirate ships have increased speed over their standard counterparts--a Pirate Gunboat or Pirate Frigate can keep pace with a Clipper with no problem, so ensure that they are kept well away from your shipping lanes by whatever means!
The clipper ship evolved out of the schooner, and dominated global trade from its appearance in the mid-1800s until the Suez Canal opened in 1869. Three-masted, square-rigged, long, and narrow, the clipper ship was a thoroughbred built for speed--even the name comes from a term for going fast.
Clipper ships were not actually bulk transports, which was the job of a different type of ship called a windjammer. As their speed suggests, clippers specialized in hauling small amounts of cargo which needed to move fast--most famously tea. They were short-lived ships due to their hard working lives; few had long careers, and even fewer survive today. 
Game Update 5 (September 10, 2019):