A jetty is a narrow structure that's built to stretch from land out into the water. Some jetties act as docks or piers for boats.
A man-made jetty is often a protective barrier against beach erosion, and it also provides pedestrians access to boats or fishing areas. Jetties are generally made of concrete, wood, or stone. Jetty comes from the French jetee, which means both "a throw" and "a projecting part of a structure," or "a part that's 'thrown out' beyond the main structure."