(1) See
iOS 8 Wave prank.
(2) A ripple or undulation. All electromagnetic radiation, including radio signals, light rays, x-rays, and cosmic rays, as well as sound, behave like rippling waves in the ocean. To visualize a wave, take a piece of paper and keep drawing a line up and down while pulling the paper perpendicular to the line. Modulate the line by making it different lengths as you draw it with the paper moving, and notice the resulting pattern. See
wave-particle duality and
wavelength.