How is a rare disease categorized according to the provided information?

A rare disease is defined as one that affects fewer than 200,000 people in the United States. This definition is in accordance with the Orphan Drug Act, which aims to encourage the development of treatments for diseases that affect such a small portion of the population. By categorizing a disease this way, it helps ensure that individuals suffering from these relatively uncommon conditions can receive specialized attention and resources for research and drug development. Therefore, when determining if a disease qualifies as rare, the key threshold is this 200,000-person mark. Options that specify larger populations do not fit within the established definition of what constitutes a rare disease.