Term: Dual-Weapon Fighting / Off-Hand Attacks

When you are using an Attack from the Attack Action, you can use the weapon in another hand or that is or readily available (such as a tail natural weapon with a blade or stinger), attacking with it for free after the main hand attack. This is an Off-Hand Attack.
Only weapons with the Agile trait can be used for an Off-Hand attack unless a feat, feature, or talent gives you the ability to do so otherwise.
Your Off Hand attack must come after a main-hand attack. Off-Hand Attacks), and their damage damage dice is reduced by 1 step (1d12 becomes 1d10, then 1d8, 1d6, 1d4, then just 1). Natural weapon off-hand attacks do not add Half-Proficiency, if it's available. Finally, you do not add your Attribute bonus to the damage of the attack. Bonuses to the attack's damage from other sources (such a s enchants) are unchanged.
In order to add those numerical modifiers back to the weapon's damage, one needs a talent or fighting style that grants such, like Multiweapon Fighting.