When two progressive waves of the same wavelength and amplitude traveling with the same speed through a medium in opposite directions and superimpose upon each other, they give rise to a wave which is called a stationary wave.
In stationary waves, there are certain points where the amplitude of vibration is always zero. These points are known as nodes. Midway between these nodes, there are other points where the amplitude of vibration is maximum. These points are known as antinodes. The formation of the stationary wave along with nodes and antinodes is shown in the figure.