The Underground refers to a network of secret routes and safe houses used by enslaved people in the United States during the 19th century. This system helped them escape to free states and Canada, where slavery was illegal. The network was supported by abolitionists and sympathizers who provided shelter, food, and guidance. Key figures in the Underground included Harriet Tubman, who made numerous trips to rescue enslaved individuals, and Frederick Douglass, who advocated for abolition. The Underground was not a single organization but rather a collaborative effort among many people committed to ending slavery and promoting freedom.