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This is standard statistical terminology, where "average" is a general term used to describe a central tendency of data. Canonical example averages are arithmetic mean, median, mode.

In popular usage, this has become muddled because the arithmetic mean is also an estimate of the peak/center of a Gaussian distribution from a sample distribution.

Note that "arithmetic mean" is what you colloquially call "average" and think of as "the mean" but it is not in any way the only "mean", either.

See e.g. https://en.wikipedia.org/wiki/Average