Generally speaking, a standing wave is a wave that remains in a constant position. There are two ways that standing waves are produced. One way a standing wave is created is when the medium and the wave are moving in opposite directions. Another way they are created is through a stationary medium and two interfering waves. Standing wave patterns are the result of the repeated interference of two waves of identical frequency while moving in opposite directions along the same medium. During this interference resonance is created in the system. This interference creates an optical illusion of the entire system moving in a simple harmonic motion.
Standing waves are produced whenever two waves of identical frequency interfere with one another while traveling opposite directions along the same medium. Standing wave patterns are characterized by certain fixed points along the medium which undergo no displacement. These points of no displacement are called nodes. Nodes are always located at the same location along the medium. This in turn, gives the entire wave pattern an appearance of standing still (hence the name "standing waves".) Nodes are the result of the destructive interference of the two interfering waves. At all times in a standing wave, and at all nodal points, both waves interfere to completely destroy each other, then producing a node. Midway between every consecutive nodal point is points which undergo maximum displacement; these points are referred to as antinodes. Antinodes are points along the medium which oscillate back and forth between a large positive displacement and a large negative displacement.