Habitat - The specific geographical area or physical environment that is inhabited by an organism or a population of organisms.⏎
Immunization - The process of strengthening the body’s defense against a particular infectious agent, often accomplished by receiving a vaccine.⏎
Host - An organism that harbors a parasite or another organism where there is a symbiotic relationship between the two organisms. In some cases, the relationship is commensal, or mutually beneficial, but in the case of a parasite and host, the host may be hurt by the parasite's presence.⏎
Germ Theory - A theory in medicine stating that microorganisms are the causative agents of infectious, contagious diseases.⏎
Microbe - Sometimes referred to as a microorganism, a microbe is an organism that is microscopic and thus invisible to the naked eye.⏎