where do you think I can distinguish passive skills/battle stances (in moment of skill choosing)?
You can check the meanings of skill/stance in wikipedia.
I am sure you'll see the common between them.
Berserker Stance gives you % bonus to damage in defense. - Meaning it
boosts your damage while you're being attacked and you defend yourself - which means, that it's not an active skill.
Melee Defense gives % bonus when in the defense vs melee, but also takes from you the same % when defending yourself vs archers.
And not trying to be smartie but as far as I know, the opposite of active is passive, you know ? So you can either call it skill or stance. Whatever makes you feel better
Edit: Thank you, Crassus!