(number theory) The mathematical theorem which states that, for given odd prime numbers p and q, the question of whether p is a square modulo q is equivalent to the question of whether q is a square modulo p.

(mathematics) A number (real or complex) which is a solution to an equation of the form x²+Bx+C=0 for some integers B and C. For example 42, or 2+3i, or 1+√/2.

Having the shape of a quadrangle; in the shape of a quadrangle.

Happening every four years. / Lasting for four years.

A four-year period, a quadrennium.

Abbreviation of quarto.

A slotted plate for carrying the gears of a lathe. / A Petri dish, divided into four, and containing agar and other materials, used in the identification of bacteria.

paper marked out with squares

(of a sound system) Employing four independent channels or speakers.

(mathematics) A type of average, calculated as the square root of the mean of the squares, ie. Q=√x_1²+x_2²+...+x_n²/n.