Quadrature

(astronomy) The right-angle physical alignment of the sun, moon, and earth.
(mathematics) The construction of a square whose area is equal to that of a given surface. The process of calculating a definite integral.
(physics) State of being separated in phase by 90°, or one quarter-cycle. Also known as phase quadrature.

The condition in which the phase angle between two alternating quantities is 90°, corresponding to one-quarter of an electrical cycle. The electric and magnetic fields of electromagnetic radiation are in space quadrature, which means that they are at right angles in space. See also Absorption of electromagnetic radiation.

The current and voltage of a perfect coil are in quadrature because the coil current lags behind the coil voltage by exactly 90°. The current and voltage of a perfect capacitor are also in quadrature, but here the current leads the voltage by 90°. In these last two cases the current and voltage are in time quadrature.