The number of digits that are meaningful: they have an accuracy matching our measurements, or are simply all we need.
Example: we measure the garden to within 1 meter.
Our calculations give an area of 58.37215 m2
But that is way more digits than our accuracy of measurement, so we decide to use 2 significant digits.
Our final result is 58 m2 (the two significant digits are 5 and 8).
More Examples:
• when we show a result like 4.500 we are saying we know it isn't 4.499 or 4.501
• but a number like 300 suggests we know it isn't 200 or 400
We can add a "plus/minus" (±) value to show our level of accuracy:
Example: 300 ± 10 says we know it is between 290 and 310
Have a play: