What is Fugitive Slave Clause?

Legal Definition
The Fugitive Slave Clause of the United States Constitution, also known as either the Slave Clause or the Fugitives From Labor Clause, is Article IV, Section 2, Clause 3, which required a "person held to service or labour" (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 forbids slavery, made the clause mostly moot.
-- Wikipedia