A rare disease is a health condition that affects a small percentage of the population, typically defined as fewer than 200,000 people in the United States. These diseases can be genetic, infectious, or autoimmune, and often have limited treatment options due to their low prevalence. Many rare diseases are not well understood, leading to challenges in diagnosis and management. Organizations like the National Organization for Rare Disorders (NORD) work to raise awareness and support research efforts to improve the lives of those affected by these conditions.