Which of the following best defines "Medicare"?

Medicare is best defined as a federal program primarily for individuals aged 65 and older because it was established to provide health insurance coverage to senior citizens, helping them with the costs of medical care. This program plays a crucial role in ensuring that older adults have access to necessary healthcare services without the burden of prohibitive costs.

While other programs exist to assist different populations, such as uninsured children or low-income families, Medicare specifically targets the aging population. It includes different parts that cover hospital insurance, medical insurance, and prescription drug coverage, all designed to meet the healthcare needs of seniors. Therefore, defining Medicare in the context of its focus on older adults accurately captures its primary purpose and function within the U.S. healthcare system.