It means the neutral line in the wall has a current differential as compared to ground. A good electrical system would not have a differential like that, it would have zero differential between neutral/ground.
With modern US wiring, at a 120v socket, neutral is usually white wire, and ground is usually green or bare copper uninsulated.
I'd find the fault in the house wiring, or call an electrician to fix it. It has the potential to be dangerous.