Immune system: refers to the collection of mechanisms involving cells, tissues and organs that protects organisms against disease by identifying and killing pathogens and tumour cells.
Immunity: to the state or quality of being resistant (immune) from infectious disease, either by virtue of previous exposure (adaptive immunity) or as an inherent trait (innate immunity).
Immunization: the process of producing a state of immunity in a subject.
Immunogen: A substance capable of eliciting an immune response. All immunogens are antigens, but some antigens are not immunogens (e.g., haptens).
Immunogenicity: The capacity of a substance to induce an immune response under a given set of conditions.
Innate immunity/inborn/genetic/heritable: Nonspecific host defences that exist prior to exposure to an antigen and involve anatomic, physiologic, endocytic and phagocytic and inflammatory mechanisms.
Adaptive immunity/acquired/specific: Host defences that are mediated by B and T cells following exposure to antigen and that exhibit specificity, diversity, memory and self/non-self-recognition.