* "Cyfrwng" is a more general term for "mean" as in "average". For example: "The mean temperature was 15 degrees Celsius" would be "Y tymheredd cyfrwng oedd 15 gradd Celsius".
* "Cymedr" is more specific to the meaning of "average" in the context of "mediocre" or "not particularly good or bad". For example: "The movie was just average" would be "Y ffilm oedd yn gymedr".
It's important to consider the context of the sentence when translating "mean" into Welsh.
Let me know if you have a specific sentence you'd like translated, and I can help you with the most accurate translation!