The Poise refers to the ability of a character to withstand other attacks during the execution of a Skill without canceling it.
In some games, this is also known as Hyper-Armor.
When a character starts playing a Skill, its Poise Armor is filled. If during the execution of this Skill the character receives any attack from an enemy, the Poise Armor will be reduced by the Poise Damage of the enemy's Skill.
Any subsequent attacks will also damage the Poise Armor. If it reaches zero or less, the character's Skill will be automatically canceled at that frame and will play a Hit Reaction.
By default, all Skills have a Poise Armor of 1 and a Poise Damage of also 1 unit. This means that any attack can be interrupted by an enemy's attack. If you want an enemy to withstand more than one attack, increase the Damage Armor.
The Poise value of a character can be visualized at runtime by simply selecting the character object and looking at the Inspector window.
At the very bottom of the character component, there's a Poise gauge that is filled whenever the character executes a Skill. This gauge diminishes with each attack received.