정 means rightness / truth 말 means speaking / story The opposite / antonym of "정(말)" is 거짓(말) (lie) 정말 means really 진 means genuine 짜 means a thing / a stuff The opposite / antonym of "진(짜)" is 가(짜) (fake) 진짜 means really They mean "Really". They have no difference. I'd say 진짜 is a bit stronger than 정말 and 정말 sounds a bit more chill. Both words may be used colloquially, but 정말 would be more formal than 진짜. But 진짜 itself is not too much of an informal word.