Stray votlage

[wingedfish]

your right in that it stands for ground, and also right in that most of the equipment doesn't have a ground.

A little off topic but a gfci monitors current in and out on hot and neutral (simplistic terms, there is no in and out etc) if more goes out then comes back on neutral, usually do to a short to ground, then it trips. This explain why a gfci would trip upon the addition of a ground rod. but the problem existed before it. The more grounds the safer.