A prion is a type of infectious agent composed solely of protein. Unlike bacteria or viruses, prions do not contain any genetic material. They are known to cause a variety of neurodegenerative diseases by inducing abnormal folding of normal proteins in the brain, leading to brain damage and severe neurological symptoms. Prions are responsible for several diseases in animals and humans, including Bovine Spongiform Encephalopathy (commonly known as "mad cow disease") and Creutzfeldt-Jakob Disease. These diseases are characterized by long incubation periods and are often fatal, highlighting the unique and dangerous nature of prions in the field of infectious diseases.