The expression signifies a complete lack of understanding. When someone says something is Greek to them, they mean it is incomprehensible, similar to hearing a language they do not know. For example, a complex physics equation might be “Greek” to someone without a science background.
The phrase’s historical roots can be traced back to medieval Latin. Its enduring usage highlights the human experience of encountering information or subjects that are utterly beyond one’s grasp. Its value lies in its succinct conveyance of incomprehension, serving as a relatable idiom across various fields and contexts.