A jibe (US) or gybe (Britain) is a sailing maneuver whereby a sailing vessel reaching downwind turns its stern through the wind, such that the wind direction changes from one side of the boat to the other. For square-rigged ships, this maneuver is called wearing ship.
In this maneuver, the mainsail will cross the center of the boat while the jib is pulled to the other side of the boat. If a spinnaker is up, its pole will have to be manually moved to the other side, to remain opposite the mainsail. In a dinghy, raising the centerboard can increase the risk of capsizing during what can be a somewhat violent maneuver, although the opposite is true of a dinghy with a flat, planing hull profile: raising the centerboard reduces heeling moment during the manouevre and so reduces the risk of capsize.
The other way to change the side of the boat that faces the wind is turning the bow of the boat into, and then through, the direction of the wind. This operation is known as tacking or coming about. Tacking more than 180° to avoid a jibe is sometimes referred to as a 'chicken jibe'.
Many sailboats are significantly faster sailing on a broad reach than running (sailing straight downwind). Thus the increased speed of a zig-zag course of alternating broad reaches can more than make up for the extra distance it takes over a straight downwind course. Jibing is also common in racing, which often use a triangular course marked with buoys; the most direct way of rounding a buoy may be to jibe.
Jibing is a less common technique than tacking, since a sailboat can sail straight downwind, whereas it cannot sail directly into the wind and has to sail a zig-zag course at alternating angles into the wind. However, a jibe can generally be completed more quickly than a tack because the boat never turns into the wind, and thus a jibing boat's sails are always powered whereas a tacking boat's luffing sails are un-powered while the bow crosses through or into the direction of the wind.