What is X and Y and Lissajous on an Oscilloscope?

[FAQ Team]

X and Y are the 2 axis on the scope screen or "graticule".

X is the horizontal axis, which represents the time the waveform is shown over.
Y is the vertical axis on which the wave height or "amplitude" is shown.

Tip, Y is high, X is a cross (across)

They are also labeled on each channel of 2 channel scopes as Ch1X and CH2Y so 2 signals can be input and compared on the screen using the X-Y control.
One signal drives horizontally X the other vertically Y.

So at its simplest if both signals were the same level and in phase and both channels were set to same input sensitivity the result would be a straight line at 45 degrees from bottom left to top right of the screen. Different shapes and directions of lines occur with differences between the 2 signals. For example if they were still both the same level but 180 degrees out of phase there would still be a straight line at 45 degrees but from bottom right hand corner to top left hand corner. These are Lissajous figures.