Source : Webster's Revised Unabridged Dictionary (1913)

Invariance \In*va"ri*ance\, n. (Math.)
   The property of remaining invariable under prescribed or
   implied conditions. --J. J. Sylvester.

Source : WordNet®

invariance
     n : the quality of being resistant to variation [syn: {invariability},
          {invariableness}] [ant: {variability}, {variability}]