Quote Originally Posted by Keld Denar View Post
If thats the "official definition" of offhand, then which attack is your offhand if you attack with armor spikes and a mouthpick weapon? I mean, by that definition, it has to be a hand, so in theory, if you don't use a hand, you don't have an offhand, right?

No. Its simpler than that. There is no offhand without TWFing. 3.0 had handedness. 3.5 eliminated it. Its errata by ommision, if anything.
An off-hand attack (as per TWFing) is not the same as an attack with the off hand. The off hand is the non-dominant hand. It's confusing terminology, and most likely, the glossary entry is a remnant from 3.0, but since it's there, we can't just ignore it while discussing RAW; chirality is still a thing. Off hand is defined in the rules (unless you want to claim the glossary isn't part of the rules).

Attacking with armor spikes (or any other weapon that isn't wielded in the hand) has nothing to do with handedness.