Windward is the direction upwind from the point of reference, i.e. towards the direction from which the wind is coming. Leeward is the direction downwind from the point of reference, i.e. along the direction towards which the wind is going.
The leeward region of mountains generally remains dry as compared to the windward region. The side of a ship that is towards the leeward is its "lee side". If the vessel is heeling under the pressure of crosswind, the lee side will be the "lower side". During the Age of Sail, the term weather was used as a synonym for windward in some contexts, as in the weather gage.
The name "lee" comes from the middle-low German word /l?/ meaning "where the sea is not exposed to the wind" or "mild". The terms Luv and Lee (engl. Windward and Leeward) have been in use since the 17th century.
Windward and leeward directions are important factors (points of sail) to consider when sailing a sailing ship. Other terms with broadly the same meaning are widely used, particularly upwind and downwind.
The windward vessel is normally the more maneuverable vessel. For this reason, rule 12 of the International Regulations for Preventing Collisions at Sea, applying to sailing vessels, stipulates that where two are sailing in similar directions in relation to the wind, the windward vessel gives way to the leeward vessel.
In warfare, a square-rigged warship would often try to enter battle from the windward direction (or "hold the weather gage"), thus gaining an important tactical advantage over the opposing warship – the warship to windward could choose when to engage and when to withdraw. The opposing warship to leeward could often do little but comply without exposing itself unduly.
Leeward and windward refer respectively to what a game stalker would call downwind and upwind. The terms are used by seamen in relation to their ships but also in reference to islands in an archipelago and to the different sides of a single island. In the latter case, the windward side is that side of an island subject to the prevailing wind, and is thus the wetter side (see orographic precipitation). The leeward side is the side protected by the elevation of the island from the prevailing wind, and is typically the drier side of an island. Thus, leeward or windward siting is an important weather and climate factor on oceanic islands.
In the case of an archipelago, windward islands are upwind and leeward islands are the downwind ones.
In these contexts the terms windward and leeward are not used.