Reflex refers to the regular response of an organism to stimuli with the help of the nervous system. Unconditioned reflex is an innate reflex that can be learned without learning. It is a simple reflex without any conditions, and it is an instinctive behavior. Conditioned reflexes are learned by organisms in their acquired life, only those that occur under certain conditions.
Xiao Wang went out to work and accidentally lost his belongings. He didn't eat for a few days. When he was very hungry, his stomach groaned and he swallowed when he saw food fits the definition of unconditional reflection.