One of the hottest trends in wall decoration might be a term you've never heard of. Fortunately, we're here to save you from embarrassing yourself in front of your design-savvy peers by blurting, "What is shiplap?" This horizontal pattern of interlocking wooden boards was traditionally used to build sheds and barns (but not ships, in spite of its name). Long seen as cheap weatherproofing, shiplap is now being used by designers to cover interior walls.