Definitions of some variables

I’m using the RTDE module to save the data.
I want to get the voltage and current of the robot.
There are some similar names.
For instance, actual_main_voltage, actual_robot_voltage and actual_joint_voltage. It seems they are very close to each other, around 48 V.
As for the current: actual_robot_current, actual_current. they are totally different from each other.

Is there anyone who can tell me the difference between each other?

Thanks!