Phasor

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.

Phasor Media

An example of series RLC circuit and respective phasor diagram for a specific $ω$ . The arrows in the upper diagram are phasors, drawn in a phasor diagram (complex plane without axis shown), which must not be confused with the arrows in the lower diagram, which are the reference polarity for the voltages and the reference direction for the current.
The sum of phasors as addition of rotating vectors
Phasor diagram of three waves in perfect destructive interference