A beautiful visualisation of standing waves of high frequency sound.
Something similar happens at the beginning of the video below with a cotton string moved by a motor at a constant frequency on one end, and fixed on the other. Then he turns on a strobe light at varying frequencies. These are not sound waves, but look very cool:
A string fixed at both ends can be found on any string instrument, like a guitar.
This video gives a clear and funny explanation on standing waves, nodes, antinodes, wavelength, fundamental frequencies and harmonics: