What does reh mean in greek?

There's no word "reh" in standard Greek. It's possible:

* It's a misspelling: Could you be thinking of a different word? If you can provide more context (e.g., where you saw it, what it was referring to), I might be able to help.

* It's a dialectal word: Greek has many dialects, some with words not found in standard Modern Greek. If it's from a specific region, knowing that would be helpful.

* It's not Greek: The word might belong to another language entirely.