Final answer:
The term for a serious condition where the body's natural immunity against disease is compromised is immunodeficiency, which includes primary forms like SCID and secondary forms like HIV/AIDS.
Step-by-step explanation:
A serious condition characterized by a defect in the body's natural immunity against disease is identified by the term immunodeficiency. This term encompasses conditions where there is a failure, insufficiency, or delay in the immune system's response, which could be either inherited (primary) or acquired (secondary).
Immunodeficiency can occur when T or B cells do not function properly or when the body doesn't produce enough antibodies. Inherited forms of immunodeficiency, such as severe combined immunodeficiency (SCID), result in virtually no adaptive immunity due to the lack of functional B and/or T cells.
Conditions like HIV/AIDS are examples of secondary immunodeficiencies, which are acquired after birth and can significantly impair the immune system. Other causes for acquired immunodeficiency can include chemical exposure, such as chemotherapy, malnutrition, extreme stress, or radiation exposure, which can destroy populations of lymphocytes.