(astronomy, celestial mechanics) An angle of 𝜏 (radians) divided by the orbital period (of a celestial body in an elliptic orbit).

(astronomy, celestial mechanics) An imaginary celestial body (corresponding to another, real, orbiting one) which orbits with constant speed along an auxiliary circle (a circle which shares a diameter with the major axis of the elliptical orbit of the corresponding real celestial body), such that its position coincides with the position of the corresponding, real celestial body when that body passes through periapsis.

(colloquial) efficient because of having nothing in excess of what is needed, and single-minded in one's objective

An average calculated after biasing values according to agreed weightings.

(statistics) Given a random sample mathbf x₁,…, mathbf x_N from an n-dimensional random variable mathbf X, a mean defined as

The mean (average) of all numbers observed, rather than that of a subsample.

The average of the squares of a set of numbers.

plural of no mean feat

(litotes) A laudable triumph of great difficulty; no small feat.

(idiomatic) A defect in character characterized by persistent nastiness, viciousness, or malevolence.