Normally I used pwcorr to have a correlation matrix. And for such a command, we have a star option.

From the description, they stated:

The star option in the pwcorr command in Stata is used to display a star (*) next to correlation coefficients that are significant at a certain level. The level of significance is determined by the user and is specified as an argument in the star option. For example, pwcorr, star(.05) will star all correlation coefficients that are significant at the 5% level or better. The option is used to quickly identify which correlation coefficients are statistically significant and which are not.
It is confused to me. What does it mean that correlation coefficients are statistically significant then?