Consider a string fixed on both ends. When the wavelength of the waves is just right, so that an integral number of half wavelengths fit into the length of the string, a standing wave forms. A standing wave is a pattern which results from the interference of two or more waves traveling in the same medium. All standing waves are characterized by positions along the medium which are standing still. Such positions are referred to as nodes .
Nodes are the result of the meeting of a crest with a trough.
This leads to a point of no displacement. Standing waves are also characterized by antinodes . These are positions along the medium where the particles oscillate about their equilibrium position with maximum amplitude. Antinodes are the result of a crest meeting a crest and a trough meeting a trough. Standing wave patterns are always characterized by an alternating pattern of nodes and antinodes.