Final answer:
The correct term that means "characterized by an exaggerated reaction to an antigen or toxin" is hypersensitivity.
Step-by-step explanation:
The term that means "characterized by an exaggerated reaction to an antigen or toxin" is hypersensitivity. Hypersensitivity is a medical term used to describe symptoms that occur in response to nonpathogenic substances. There are four types of hypersensitivities, with type I being characterized by immediate allergic reactions.