What is the fugitive slave clause?

The Fugitive Slave Clause of the United States Constitution, also known as either the Slave Clause or the Fugitives From Labor Clause,[1][2][3][4] is Article IV, Section 2, Clause 3, which requires a "person held to service or labor" (usually a slave, apprentice, or indentured servant) who flees to another state to be returned to the owner in the state from which that person escaped. The passage of the Thirteenth Amendment to the United States Constitution, which abolished slavery except as a punishment for criminal acts, made the clause mostly irrelevant.