What is the difference between AC GND,and DC GND.
Although there can be times in power circuits where AC ground is separate from DC ground, you are probably confusing the terms with AC-grounded and DC-grounded. If a circuit is grounded through a capacitor it is referred to as AC-grounded because only AC signals can pass through the cap to ground, DC levels are blocked. Whereas if a circuit is such that DC current can flow to ground, such as through a resistor, then it is considered to be DC-grounded. A classic example would be a non-inverting op amp configured with the divider feedback resistor connected through a capacitor to ground (AC-grounded), or directly to ground (DC-grounded).
This is similar to AC-coupled and DC-coupled, where a capacitor is used between two circuits to block DC and allow only the AC component to pass. An example would be one op amp circuit, the first stage, driving the second stage through a coupling capacitor (AC-coupled), or directly connected through a resistor without a coupling capacitor (DC-coupled)
