Q: What is the difference between Full Hook Up (FHU) and electric only at a campground?
A: Full hook up(FHU) is water, electric and sewer(to dump your tanks).
Electric only means no water and no dump facilities at your camp site.
WITHOUT FHU:
Freshwater: you will need to fill your fresh water tank somewhere with POTABLE water, sometimes the campgrounds have those places and sometimes not, find out beforehand.
Black/Grey tank dumping: You have no place to dump at your site, so you will need to either unhook the RV, drive it to s dump station OR carry one of those portable tanks dump into it and haul it to dump station.