What is the term when hard biscuits become soft due to exposure to air or moisture?

The term for when hard biscuits become soft due to exposure to air or moisture is called "staling." Staling is a complex process involving the migration of moisture from the air into the biscuit, which causes the starch molecules in the biscuit to recrystallize and lose their crispness. This process is accelerated by the presence of unsaturated fats in the biscuit, which can react with oxygen in the air to form rancid compounds.