Immunity: The ability of an organism to resist a particular infection or toxin by the action of specific antibodies or sensitized white blood cells.
Herd Immunity: A form of indirect protection from infectious disease that occurs when a large percentage of a population has become immune to an infection, thereby providing a measure of protection for individuals who are not immune.
Inoculation: The introduction of an antigenic substance or vaccine into the body to produce immunity to a specific disease.