The frequency of a wave is the number of times per second that a piece of the wave oscillates. The period of the wave, just as with an oscillator, is the amount of time between repetitions. The wavelength of a wave may be measured from crest to crest or from valley to valley. The amplitude of a wave describes how far the individual pieces of the medium that make up the wave move from their equilibrium positions.
Waves may be transverse as in waves on a string. In transverse waves, the motion of individual pieces that make up the whole wave is perpendicular to the motion of the wave as a whole. Waves may be longitudinal as in sound waves. In longitudinal waves, the motion of individual pieces that make up the whole wave is along the direction of the motion of the wave as a whole.
Transverse waves may be plane polarized so all the disturbances that compose the wave are confined to a plane.
Two waves may pass through each other unimpeded; this is known as superposition. When two waves do pass through each other, the resulting amplitude is the sum of the amplitude of the two waves.
Standing waves on a string are an example of resonance. Standing
waves will produce a series of nodes and antinodes. There is
no motion of the string at a node and maximum amplitude at an
antinode. The fixed ends of the string must be nodes. Standing
waves on a string occur only for frequencies or wavelengths such
that a whole number of loops fit onto the length of the string.
The length of a loop is one half a wavelength.