A room in a building, specifically a bedroom, which is perfect for sex. The atmosphere of the room, the decorations, the lighting, the smell, all put you in the mood and increase your chances of getting laid.
David's bedroom was such a slam pad. He had incense burning, a black light, a lava lamp, a comfy bed, and Pink Floyd's, Dark Side of the Moon was playing on his cd player. It took all of my willpower to not mount him on the spot.