Quadrature phase

In electrical engineering, a sinusoid with angle modulation can be decomposed into, or synthesized from, two amplitude-modulated sinusoids that are offset in phase by one-quarter cycle (p/2 radians). All three functions have the same frequency. The amplitude modulated sinusoids are known as in-phase and quadrature components.  Some authors find it more convenient to refer to only the amplitude modulation (baseband) itself by those terms.