the right term for what a lot of people call the 'average'. Usually shortened to 'mean'. Calculated with the addition of up a number of values and dividing the full total because of the number of values. For example, 1+2+3+4+5+6+7=28. The mean is 28 divided by 7, which equals 4. The mean is in contrast towards the mode and median, that are various other measures of main inclination.
the sum of the values of a random variable split by the number of values
the easy average. Hence the arithmetic mean of letter quantities could be the sum of these volumes split by n. Comparison with geometric suggest. -- C.A.B.
Mention may also be made of his chapter on inequalities, in which he proves that the arithmetic mean is always greater than the geometric mean.