Mean (the average value, 均值)
Median (the middle value, 中位数)
Mode (the most common value, 众数)
The three words are easy in Chinese because the the Chinese characters tell you what the terms mean. But the meanings of the English words may not be so obvious. It's worth thinking of a way to help remember them.
English 'mean' and 'median' are from the same Latin word 'medianus'. When it entered Old French, it lost the consonant 'd' (this is a regular change as it's between two unstressed vowels) and eventually entered English as 'mean', as early as the 14th century. This meaning was taken by the common people. Later, Latin 'medianus' entered French as a learned word, i.e. taken by the church scribes, who tried to preserve the original Latin pronunciation, so the 'd' was not omitted (even though the people on the street did not pronounce it). It's probably safe to say that the more popular or vulgar or low-status word 'mean' takes the more general meaning ("average value"), and the more learned or high-status word 'median' takes a more specialized meaning such as defined by mathematicians or statisticians as "middle value". As to 'mode', it's an entirely different word. Think of 'à la mode' or "in the fashion". What is in fashion is the most common. So 'mode' denotes the value that occurs the most in a set.
In general, it is not right to invoke etymology to explain the meaning especially a subtle one of a modern word in modern usage. That's considered an etymological fallacy. But in this case, it makes sense to use etymology to explain why 'mean' takes a more general sense while 'median' takes a more specialized one.
