The phrase "underground railway" typically refers to a secret network that helped enslaved African Americans escape to freedom in the 19th century. Synonyms for this phrase might include "underground railroad" (which is a more common variant of the phrase), "freedom railway," or even "liberty line." Other related terms could include "abolitionist network," "slave escape route," or simply "underground escape." Regardless of the specific wording used, these terms all describe a vast, decentralized network of individuals who were committed to helping slaves escape to freedom during a time when the legal and social systems of the United States still condoned slavery.