rotating phasor
And it's usage?
Are you talking about the basic phasor used in introductory AC circuit theory?
Polar coordinates are sometimes more easily visualized and if the phase of the signal is important (like in phase shifters and MPSK modulation).
If the vector is rotating, it sometimes means that its frequency is slightly different from the reference frequency. It is gaining or losing phase.
In electric motors it is sometimes used to describe the magnetic field direction.
assuming that ur question is pertaining to communication theory, phasors are used for representing the signals graphically, and it is a way of representing real signals in the complex form, u would have known that... just for convenience, the phasor gives all the information as to the orientation adn the frequency of the signal etc... especially used in the band pass and base band transformation, basic theories...
regards,
Arun.