The word itself is indication enough IMO. OVERfeeding is just that, feeding more than is healthy/necessary. Most of us in the hobby (myself included) overfeed. Not necessarily because we want to but because we grossly overestimate what a fish actually eats in the wild. Fish are opportunistic feeders, which means that they may go weeks between solid meals. Now, that isn't an excuse to forget feeding, but a reminder that our fish will be perfectly fine if we don't feed them to bursting every day. A great byproduct of overfeeding is that us with aggressive fish don't have to worry about the fish in question eating its tankmates because it is already full. But not all the time. So the real answer is: It truly depends on your fish. Watch them closely, keep their bellies full, but don't stuff them to the point that they kill themselves from indigestion.
