A measure of central tendency is a single value that attempts to describe a set of data by identifying the central position within that set of data. The mean (often called the average) is most likely the measure of central tendency that you are most familiar with, but there are others, such as the median and the mode. The mean, median and mode are all valid measures of central tendency, but under different conditions, some measures of central tendency become more appropriate to use than others.
Mean (or average)
The mean (or average) of observations is the sum of the values of all the observations divided by the total number of observations.
Median is that value of the given number of observations, which divides it into exactly two parts when the variables are arranged in ascending or descending.
A mode is that value among the observations which occurs most often, that is, the value of the observation having the maximum frequency.