Signal ground concept..

signal ground is nothing but the common signal to the particular circuit...a signal (+ve or -ve) is with respect to some common signal and that common signal is ground signal...ground doesnt mean that we are grounding the signal or we are sending the signal to some sort of ground contact... its just the signal with respect to which all the measurments are taken...

thanks so much.
can u please make it more understandable?

please differentiate between Active and Signal ground as well.

Active ground? No idea. I think your job is PCB designer right.

As i know, there have common ground & signal ground. in theory this ground are same point which 0V. But in communication, there have disturbance if no different point between signal & common ground. The rational is normally signal ground is in low voltage side. If this low voltage ground is mix with high voltage ground, Then it will affect on performance of the design. For functional, if the ground is mix together, the functional circuit still good but if the circuit have fast switching it will affected. Example, in microcontroller.

It is recommended the signal ground is design shortest possible to where the signal come from and dont simply mix between low voltage ground (signal ground) & high voltage ground