Waves can also be categorized as eitherstandingorprogressive. Progressive waves transfer energy from A to B, and so their peaks appear to move. For standing waves, they do not. In the real world, most waves occur as progressive waves - ocean waves and sound waves for example.

Standing waves occur as a special case when waves are confined in space. For progressive waves all points along the wave oscillate the same amount, this is not the case for standing waves where the amount of oscillation depends on the position. They contain special points callednodesthat do not move at all andanti-nodesthat oscillate the most. Standing waves are hard to find naturally as they only occur under certain circumstances, but musicians make use of them all the time. The strings on a guitar oscillate in a standing wave when they are plucked for example.