What is a Stance?

I see a bunch of the Skill Trees talk about different Stances and I see a whole bunch of Youtube videos trying to talk about what Stances are best for each Class. But, nothing I have found (in the game or online) has explained what a Stance even is. So if somebody could explain what exactly a Stance is and what it's good for, I would really appreciate it. Thanks.

stances are abilities for a class that can be either active (must be activated via pallet) or passive(always active) the abilities vary with class.

Alright. Hopefully the in-game descriptions will be able to explain the rest of it. Thank you very much.