A standing wave, also known as a stationary wave, is a wave that has a point called a node and does not move. Stationary waves are formed when two opposing waves that have identical frequencies and are traveling in mediums that are moving in opposite directions combine. In a stationary wave, each point on the axis has a constant amplitude. The nodes of a standing wave are areas at which the amplitudes are at a minimum. The locations on a standing wave where the amplitude is at a maximum are called antinodes. Standing waves can be formed by transverse waves, such as those created along a string. However, standing waves can also be formed by longitudinal waves, such as those formed within an air column.