The adjective leeward describes an area or side of a boat that's facing away from the wind. If you move to the leeward side of your sailboat, you're shifting to the sheltered, downwind side.
You're likely to hear the word leeward when you're on a boat, since wind direction is hugely important when you're sailing. You can, however, use it to describe any area that's protected from the wind, even when you're on land. Your tent might fare best if you pitch it on the leeward side of a valley, for example. The lee part of leeward comes from the Old English hleo, which means "shelter, defense, or protection."