wiggles

wiggles n.  [scientific computation] In solving partial
   differential equations by finite difference and similar methods,
   wiggles are sawtooth (up-down-up-down) oscillations at the shortest
   wavelength representable on the grid.  If an algorithm is unstable,
   this is often the most unstable waveform, so it grows to dominate
   the solution.  Alternatively, stable (though inaccurate) wiggles
   can be generated near a discontinuity by a Gibbs phenomenon.