all the nonzero digits of a number and the zeros that are included between them or that are final zeros and signify accuracy: The significant digits of 0.01230 are 1, 2, 3, and the final 0, which signifies accuracy to five places.

British Dictionary definitions for significant figures

significant figures

espUSsignificant digits

pl n

the figures of a number that express a magnitude to a specified degree of accuracy, rounding up or down the final figure3.141 59 to four significant figures is 3.142

the number of such figures3.142 has four significant figures Compare decimal place (def. 2)

The digits in a decimal number that are warranted by the accuracy of the means of measurement. Significant digits are all the numbers beginning with the leftmost nonzero digit, or beginning with the first digit after the decimal point if there are no nonzero digits to the left of the decimal point, and extending to the right. For example, 302, 3.20, and 0.023 all have three significant digits.