The term "endogenous" refers to something that originates from within a system or organism. In biology, it often describes processes or substances that are produced internally, such as hormones or enzymes that are generated by the body itself. This contrasts with "exogenous," which refers to factors that come from outside the system. In economics, "endogenous" can describe variables that are influenced by other variables within a model. For example, in a macroeconomic model, factors like investment and consumption can be considered endogenous because they are determined by the interactions of various elements within the economy.