Final answer:
D. Idiopathic. Idiopathic is the term that refers to a disease process that has no defined course and is of unknown origin.
Step-by-step explanation:
The term that refers to a disease process that has no defined course and is of unknown origin is idiopathic. Idiopathic diseases are those for which the cause is not currently understood. These diseases can be challenging to diagnose and treat because their origin is unknown. An example of an idiopathic disease is idiopathic pulmonary fibrosis, a condition that causes scarring in the lungs without a known cause.