Statically significant is a term used in hypothesis testing. When you test some null hypothesis, such as whether sample S1 and sample S2 have the same median, you must consider not only the observed medians but also the variance present in the samples and construct a confidence interval that helps decide whether you can reject the null hypothesis with good confidence or whether based on the observed data you cannot. Statistical significance helps quantify whether a result is likely due to chance or not. Hypothesis testing is also used to conclude whether some observed difference in sample properties of the original and synthetic data is statistically significant, so that you can be sure that it is real, not that you just got lucky (or unlucky) in your sample selection.