Definition of Significant digits:
Number of digits in a figure that express the precision of a measurement instead of its magnitude. In a measurement, commonly the in-between (embedded) zeros are included but leading and trailing zeros are ignored. Non-zero digits, and leading zeros to the right of a decimal point, are always significant. For example, the figure 239.80 has four significant digits, 925,000 has three, and 0.030677 has six.
Meaning of Significant digits & Significant digits Definition