Soul Extract is an Action Feature that allows the absorption of monster's souls upon their defeat.
Soul Extraction is an action that allows the absorption and collection of monsters' souls. Any character may perform Soul Extract, but the effectiveness is different based on their experience.
Soul Extract is almost compulsory to perform, especially to trully defeat boss monsters. Performing Soul Extract is always available at anytime on an Undead enemy, but doing so won't obtain their soul, only destroy or greatly damaging them.
Soul Extract deals Aether damage against Undead enemies, it does no damage against Undead bosses.