Quadrature

Quadrature, derived from Latin quadrare, is a term with various meanings:

• in astronomy, the line tangent to an object's orbit defines the object's quadrature. For a circular orbit, this line is 90°, or a quarter of a circle, away from the center of the orbit.
• in geometry, quadrature of the circle or squaring the circle is the problem of constructing a square and circle of equal area, impossible using only an unmarked straightedge and compass
• in mathematics, quadrature is a synonym for numerical integration
• in telecommunications, quadrature refers to signals which are separated in phase by 90° (π/2 radians)
  • Quadrature amplitude modulation (QAM) is the encoding of information into a carrier wave by variation of the amplitude of both the carrier wave and a 'quadrature' carrier that is 90° out of phase with the main carrier in accordance with two input signals.