Greek译为“希腊语”，It's all Greek to me字面意思是“这对我来说全部都是希腊语”，引申为我完全不懂。

【例句】
She tried to explain how the system works, but it's all Greek to me.
她努力解释系统如何运作，可我怎么也弄不明白。

That lecture on physics-i'd no idea what he was saying，it's all Greek to me!
那堂物理课我不知道他在说什么，我完全听不懂。