I have never heard of "over hardening". My take would be leaving the plants in the pots longer than the optimum time before setting them out. I try to harden plants off from day 1.

Not a term normally used with the process of hardening-off plants.

Likely just a term someone made up to cover plants that have been kept from transplanting for some reason for far too long so are heavily stressed - sun scorched, wind burned, too big, too small containers, root bound, blooming or even setting fruit while still in small containers, etc.

Dave

Probably a new term for a stunted plant for the reason stated by dave.

Thanks everyone, that's what I thought. :)

Wayne said it best: Just keeping the plant in the original pot for two log, when it starts getting root bound, midgitized. I have one such plant, way past hardening off, that I have no room for it. Little by little, a lot of plants that you buy from nurseries will be over hardened, root bound.