Mean - The sum of values divided by the number of values.

Median - The middle value when the values are ranked.

Mode - The most frequently occurring value.

The average of a set of numbers is the total of those numbers divided by the number of items in that set. The median and the average might be close, but they could also significantly different. It all depends on the numbers 

Mean is used to refer to arithmetic mean, one of the different types of mean. Mean and average are the same.