Significant digits and Significant figure

Significant figure and significant digits are semantically related. In some cases you can use "Significant figure" instead a noun phrase "Significant digits".

Significant figure noun - Any digit of a number that is known with certainty; any digit of a number beginning with the leftmost non-zero digit and ending with the rightmost non-zero digit (or a zero considered to be the exact value).

Significant digits and significant figure are semantically related. Sometimes you can replace phrase "Significant digits" with "Significant figure", this phrases are similar.