EEST stands for Eastern European Summer Time. It is always UTC+3.
EEST is daylight saving time. The rest of the year the same areas use EET (UTC+2).
Right now Athens uses EET (UTC+2), not EEST.
Where EEST is used
Bulgaria, Cyprus, Egypt, Estonia, Finland, Greece, Latvia, Lebanon, Lithuania, Moldova, Romania, Ukraine.
In some of these countries EEST is used only in part of the country or only part of the year.