\Vi*bra"tion\, n. [L. vibratio: cf. F. vibration.]
1. The act of vibrating, or the state of being vibrated, or
   in vibratory motion; quick motion to and fro; oscillation,
   as of a pendulum or musical string.
         As a harper lays his open palm Upon his harp, to
         deaden its vibrations.                --Longfellow.
2. (Physics) A limited reciprocating motion of a particle of
   an elastic body or medium in alternately opposite
   directions from its position of equilibrium, when that
   equilibrium has been disturbed, as when a stretched cord
   or other body produces musical notes, or particles of air
   transmit sounds to the ear. The path of the particle may
   be in a straight line, in a circular arc, or in any curve
   whatever.
Note: Vibration and oscillation are both used, in mechanics,
      of the swinging, or rising and falling, motion of a
      suspended or balanced body; the latter term more
      appropriately, as signifying such motion produced by
      gravity, and of any degree of slowness, while the
      former applies especially to the quick, short motion to
      and fro which results from elasticity, or the action of
      molecular forces among the particles of a body when
      disturbed from their position of rest, as in a spring.
{Amplitude of vibration}, the maximum displacement of a
   vibrating particle or body from its position of rest.
{Phase of vibration}, any part of the path described by a
   particle or body in making a complete vibration, in
   distinction from other parts, as while moving from one
   extreme to the other, or on one side of the line of rest,
   in distinction from the opposite. Two particles are said
   to be in the same phase when they are moving in the same
   direction and with the same velocity, or in corresponding
   parts of their paths.