mean square deviation

Mean Mean, a. [OE. mene, OF. meiien, F. moyen, fr. L. medianus that is in the middle, fr. medius; akin to E. mid. See {Mid}.] 1. Occupying a middle position; middle; being about midway between extremes. [1913 Webster]

Being of middle age and a mean stature. --Sir. P. Sidney. [1913 Webster]

2. Intermediate in excellence of any kind. [1913 Webster]

According to the fittest style of lofty, mean, or lowly. --Milton. [1913 Webster]

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. [1913 Webster]

{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. [1913 Webster]