That's Greek to me or it's (all) Greek to me is an idiom in English referring to an expression that is difficult to understand for the sayer. It is commonly a complex or imprecise verbal or written expression or diagram, often containing excessive use of jargon, dialect, mathematics, science, or symbols. Although to some it may seem an insult, the metaphor simply refers to the Greek language (either ancient or modern) as typifying foreign communication, written or spoken, and may be a dead metaphor, one that has lost its original understood meaning.