1.NounA digit that is meaningful with respect to the precision of a measurement; that is, excluding any leading zeroes, trailing rounding or placeholder zeroes, and non-zero digits not warranted by the accuracy of a derivation or measurement.
"The speed was calculated by dividing 2314 metres by 71 seconds and reported as 32.5915 m/s, but since both the distance and time were measured only to the nearest whole number, there were actually only two significant figures in this result, i.e. 32."
2.NounUsed other than figuratively or idiomatically: see significant, figure.