JIB

A jib is a triangular staysail that sets ahead of the foremast of a sailing vessel. Its tack is fixed to the bowsprit, to the bow, or to the deck between the bowsprit and the foremost mast. Jibs and spinnakers are the two main types of headsails on a modern boat.

Boats may be sailed using a jib alone, more commonly jib(s) make a minor direct contribution to propulsion, compared to a main sail. Generally, a jib's most crucial function is as an airfoil, increasing performance and overall stability by reducing turbulence on the main sail's leeward side.

On boats with only one jib, it is common for the clew of the jib to be further aft than the mast, meaning the jib and mainsail overlap. An overlapping jib is called a genoa jib or simply a genoa (see illustration). These are efficiently used when reaching more broadly than a close reach. Alternatively, a boat may carry smaller jibs, to compensate aerodynamics when the main sail is reefed; these more rugged sails are called storm jibs or spitfires.

On a boat with two staysails the inner sail is called the staysail, and the outer (foremost) is called the jib. This combination of two staysails is called a cutter rig (or in North America a yankee pair) and a boat with one mast rigged with two staysails and a mainsail is called a cutter.

On cruising yachts, and nearly all racing sailboats, the jib needs to be worked when tacking. On these yachts, there are two sheets attached to the clew of the jib. As the yacht comes head to wind during a tack, the active sheet is released, and the other sheet (the lazy sheet) on the other side of the boat is pulled in. This sheet becomes the new active sheet until the next tack.

...
Wikipedia