"Unblockable attacks" refers to moves or strikes in a game or fight that cannot be defended or protected against. They are attacks that opponents cannot block or counter with their usual defensive techniques.
Full definition
If it is used mid-way through a fight, your officer will deliver a
powerful unblockable attack against the person with the icon on their head.
Why didn't I roll out of the way of
that unblockable attack?
During combat it works pretty well as it lets you close the gap on enemies with guns so you can get your sword out, and it lets you avoid the more powerful,
unblockable attacks, although sometimes it can feel a little unresponsive.
However, it's not as simple as that, you see, because in Risen 2 enemies often have
unblockable attacks.
But with Just Guard, a top player can parry a string of hits,
unblockable attacks and worse.