A longitudinal pressure wave produced by the vibration of molecules in an elastic medium, which can be a liquid, solid, or gas. As the molecules are set in motion, they radiate outwards, colliding into other molecules (compression), then move apart farther than their equilibrium distance (rarefaction), travelling in this manner until they stimulate a sound receptor organ, such as an ear or tactile organ.The receptor translates the mechanical energy of the pressure wave to electrochemical energy of a nervous system, which stimulates a hearing or tactile sensation in the receiving organism; a body of water that is usually broad, elongate, and parallel to the shore between the mainland and one or more islands, e.g., Long Island Sound .