what is mean deviation ?

Average of absolute differences (differences expressed without plus or minus sign) between each value in a set of values, and the average of all values of that set. For example, the average (arithmetic mean or mean) of the set of values 1, 2, 3, 4, and 5 is (15 ÷ 5) or 3. The difference between this average (3) and the values in the set is 2, 1, 0, -1, and -2; the absolute difference being 2, 1, 0, 1, and 2. The average of these numbers (6 ÷ 5) is 1.2 which is the mean deviation. Also called mean absolute deviation, it is used as a measure of dispersion where the number of values or quantities is small, otherwise standard deviation is used.