one point on Smith chart: what does it represent?

Hi

one point on Smith chart: what does it represent?

I mean if we do some measurement or simulation on a passive interconnect structure on a single frequency, we get one point on the Smith chart.
What does it tell?- S_xx parameter real/imag, termination value (for S11 and S22)...?
how to read these values from the chart?

what does tell about an S21 insertion loss on a PCB interconenct? Some people say that the Smitch chart can be used only to display the reflection coefficient S11, but in some datasheets and software results I saw S21 on a Smith chart.

I am a digital design engineer, and I use S-parameters for passive-PCB-traces and connectors. What is the advantage to view them on a smith chart?

A smith chart is a four dimensional plot. It maps the 2 dimensions of the impedance plane into the two dimension of the reflection coefficient plane. A point can represent either a signal impedance value, or a single relection coefficient value, depending on your point of view.

In the world of complex variables, it is technically called a bilinear transform.