n. As used in formulæ of mathematics and engineering, theta (θ) usually denotes:n. the entropy, or thermodynamic function or factor by which the absolute temperature is to be multiplied to indicate an amount of heat energy.n. The angle, in angular measure, or at the center, through which a radius vector has swept from a zero position, or through which a line has swept in a rotation.n. A letter of the Greek alphabet corresponding to the English th in thin, etc.n. A sort of complication of an exponential function, being expressed by a series from n =—∞ to n = + ∞ of terms the logarithm of each of which is na + 2 na. A theta function of several variables, x1, x2, … xn, is Σ exp. (φ + Σmxn xn), where φ is a quadratic function of the constants m1, m2, … mn.n. A function which occurs in probabilities, and is expressed by the integral fe—tdt.