What is "vectorscope"

n. A special oscilloscope that displays an X-Y plot of two signals so as to indicate their relationship.

A vectorscope is a special type of oscilloscope used in both audio and video applications. Whereas an oscilloscope or waveform monitor normally displays a plot of signal vs. time, a vectorscope displays an X-Y plot of two signals, which can reveal details about the relationship between these two signals. Vectorscopes are highly similar in operation to oscilloscopes operated in X-Y mode; however those used in video applications have specialized graticules, and accept standard television or video signals as input ( demodulating and demultiplexing the two components to be analyzed internally).