It means to be set free from the control of another. The most famous act of emancipation in American history freed millions, and it was issued as a wartime military order.
Emancipation is the act of freeing someone from bondage, control, or oppression. It comes from the Latin emancipare, which in Roman law meant releasing a person from the formal authority of the head of a household.
The defining American instance is the Emancipation Proclamation. On January 1, 1863, in the middle of the Civil War, President Lincoln declared that enslaved people in the Confederate states were free. It was framed as a military measure aimed at the rebelling states.
Its reach was limited at first. The Proclamation did not free enslaved people in the border states loyal to the Union, and it could only be enforced as Union armies advanced. Freedom arrived for many only when the troops did, and for some, much later.
True, universal abolition required the Constitution itself. The Thirteenth Amendment, ratified at the end of 1865, abolished slavery everywhere in the United States for good, finishing what the Proclamation began.