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Bare hands is defined on page 12 of the rules:
Rules, page 12 wrote:
The player must also declare which equipped weapon his hero is using.
Heroes may either attack with one equipped weapon or their bare hands.
A hero attacking with his bare hands can only target an adjacent space
and rolls only the blue attack die for his attack.
So, any attack not using a weapon (even if one is equipped) is a bare hands attack, using only the blue die and having no ablities (apart of course from this monk ability).
It also follows that since shields are not weapons, you can wield two shields and attack bare handed.