What is abstract reasoning?

abstract reasoning is the ability that defines formal operational stage in piaget's theory of development

abstract reasoning, in the simplest terms, is the ability to reason or predict certain outcomes.

this is generally referred to in the context of piaget's theory of cognitive development, e.g. sensorimotor stage to formal operational stage. the defining characteristic of the formal operational stage is that the child, generally 12+, can reason or think about an scenario and predict what might happen.