Waves are disturbances that transfer energy through a medium from one point to another without transferring matter. There are two main types of waves: transverse waves, where the medium moves perpendicular to the wave direction, and longitudinal waves, where the medium moves parallel to the wave direction. Key wave properties include wavelength, frequency, amplitude, and speed. The energy of a wave depends on its amplitude, with higher amplitudes corresponding to more energy. Waves can change direction through reflection at surfaces, refraction when entering a new medium, and diffraction bending around obstacles.