What is meant by t2 flair hyperintense foci in brain ?

Various causes: T2 flair is a highly sensitive but not very specific imaging protocol in mri. Without an idea of what you are looking for, the differential becomes very broad. Assuming you are a healthy 19 year old, you could see these findings with migraine, hypertension, a recent viral illness, lymes" disease, CNS infammation, etc. You should see the physician who requested the study and discuss the results.