Medium

Medium = neither large nor small, neither tall nor short, etc.: ‘The waiter was of medium height and walked with a slight limp.’

Average = calculated by adding a set of quantities together and then dividing this total by the number of quantities in the set: ‘The average score was about 6 out of 10.’ ‘Price of gas has increased on average about 1%.’

If someone’s level of skill or ability is neither high nor low, it is average: ‘His work has been above the average.’ ‘My ability in English is about average.’