(it's) (all) Greek to me
This might as well be a foreign language, because I don't understand it at all. The phrase comes from Shakespeare's play Julius Caesar. Can you make sense of these instructions? It's all Greek to me!
be all Greek to someone
BRITISH, AMERICAN or be Greek to someone
AMERICANIf you say that something is all Greek to you, you mean that you do not understand it at all. I've no idea what it means — it's all Greek to me. I don't understand legal jargon — it's all Greek to me. Note: The idea behind this expression is that Greek is very difficult to learn and understand, especially because it uses a different alphabet from most other European languages.