Originally Posted by fairbank56
While the DC negative (DC grounded conductor) may be connected to ground, they are not the same. DC grounding conductors are normally non-current carrying.
Fair. But I'm still not sure which one he was asking about. I consider it safe to assume that when someone says ground, especially in a DC system they mean return, or in this case battery (-). I also suspect this text was trying to lay out what ground is in a general sense which blurs the lines between earth, return, (-) etc.
On and I missed the most obvious example of where ground can sink or source current - AC power. In your house the neutral line, which is supposed to be connected to earth ground, both sinks and sources current. Also if the hot wire accidentally hits something that's grounded then ground will both sink and source current.