Mean, a.
 1. Occupying a middle position; middle; being about midway between extremes.
    Being of middle age and a mean stature.   --Sir. P. Sidney.
 2. Intermediate in excellence of any kind.
    According to the fittest style of lofty, mean, or lowly.   --Milton.
 3. Math. Average; having an intermediate value between two extremes, or between the several successive values of a variable quantity during one cycle of variation; as, mean distance; mean motion; mean solar day.
 Mean distance (of a planet from the sun) Astron., the average of the distances throughout one revolution of the planet, equivalent to the semi-major axis of the orbit.
 Mean error Math. Phys., the average error of a number of observations found by taking the mean value of the positive and negative errors without regard to sign.
 Mean-square error, or Error of the mean square Math. Phys., the error the square of which is the mean of the squares of all the errors; -- called also, mean square deviation, mean error.
 Mean line. Crystallog. Same as Bisectrix.
 Mean noon, noon as determined by mean time.
 Mean proportional (between two numbers) Math., the square root of their product.
 Mean sun, a fictitious sun supposed to move uniformly in the equator so as to be on the meridian each day at mean noon.
 Mean time, time as measured by an equable motion, as of a perfect clock, or as reckoned on the supposition that all the days of the year are of a mean or uniform length, in contradistinction from apparent time, or that actually indicated by the sun, and from sidereal time, or that measured by the stars.