What term describes an infection or disease that originates within the body?

The term that describes an infection or disease originating within the body is "endogenous." This term is used in medicine to refer to conditions caused by factors that are internal to the individual, such as a malfunctioning organ or the body’s own microbiome when it becomes pathogenic. For example, certain conditions like autoimmune diseases occur when the immune system mistakenly attacks the body’s own cells.

In contrast, other terms such as exogenous refer to factors that come from outside the body, while contagious specifically pertains to diseases that can be transmitted from one individual to another, often focusing on infections caused by pathogens. Infectious is a broader term that refers to diseases caused by pathogens, but it can encompass both exogenous and endogenous sources. Thus, the specificity of "endogenous" is what makes it the correct term for infections or diseases that originate from within the body.