When considering quadrature modulation, the x axis is called the I (in-phase) axis, and the y axis is called the Q (quadrature) axis. Polar modulation makes use of polar coordinates, r (amplitude) and Θ (phase).
In quadrature modulation, the x-axis is known as the I (in-phase) axis, while the y-axis is identified as the Q (quadrature) axis. For polar modulation, polar coordinates are employed with r (amplitude) and Θ (phase).