I had mri scan and one of the impressions indicated is "non-specific, punctate, non-enhancing, t2wi/flair-hyperintense signal in the left frontal corona radiata." what does it means?

In absence of visualizing directly the films, it is impossible to histopathologically characterize the described finding. This could be congenital or acquired, potentially infectious or inflammatory, perhaps due to prior trauma, to mention a few thoughts relevant to your age. Best to seek out the radiologist and obtain a direct discussion regarding possible correlations.