any digit of a number that is known with certainty and that has a distinct numerical meaning, but not a zero at the beginning or end that is a placeholder; also called signficant figure
(sĭg-nĭf'ĭ-kənt) 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.