Phasor

complex number that represents a sinusoidal function

A phasor is a tool in mathematics. It is used to show numbers in a different coordinate system. Certain electronic components have models that can be described more easily by the use of phasors. Inductors add a +90º "phase", while capacitors add -90º "phase". Both elements work on the imaginary axis. Resistors have 0º "phase", and are considered real.